Digital load control system providing power and communication via existing power wiring

ABSTRACT

A load control system comprises a load control device for controlling an electrical load receiving power from an AC power source, and a controller adapted to be coupled in series between the source and the load control device. The load control system may be installed without requiring any additional wires to be run, and is easily configured without the need for a computer or an advanced commissioning procedure. The load control device receives both power and communication over two wires, and the controller generates a phase-control voltage that has at least one timing edge in each half-cycle, and transmits digital messages by modulating a timing edge of the phase-control voltage relative to a reference edge. The controller may be operable to receive inputs from a plurality of different input devices, and the load control device may be operable to control a plurality of different loads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application of commonly-assignedU.S. Provisional Application No. 61/587,346, filed Jan. 17, 2012,entitled DIGITAL LOAD CONTROL SYSTEM PROVIDING POWER AND COMMUNICATIONVIA EXISTING POWER WIRING, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a load control system for controllingthe amount of power delivered to an electrical load, such as a lightingload. More particularly, the present invention relates to a “two-wire”load control system having load control devices that receive both powerand communication over two wires from a digital controller that iseasily configured without the need for a computer or an advancedcommissioning procedure. In addition, the present invention relates to atwo-wire load control system having a plurality of load control devicesand a digital controller that may be installed in a pre-existingelectrical network without requiring any additional wiring. Further, thepresent invention relates to a two-wire load control system havingcontrollers that respond to a plurality of input devices and transmitdigital messages and power over two wires to load control deviceswithout interfering with other control devices on the electricalnetwork.

Description of the Related Art

In order for a gas discharge lamp, such as a fluorescent lamp, toilluminate, the lamp is typically driven by a ballast. The ballast maybe mounted in a lighting fixture in which the fluorescent lamp islocated, or to a junction box adjacent the lighting fixture. Electronicballasts receive alternating-current (AC) mains line voltage from an ACpower source and convert the AC mains line voltage to an appropriatevoltage waveform to drive the lamp. Many ballasts are simply switching(or non-dim) ballasts that are only able to turn the connectedfluorescent lamp on and off. To control a switching ballast, a standardwallbox-mounted mechanical switch is simply coupled in series electricalconnection between the AC power source and the ballast, such that a userturns the fluorescent lamp on and off by toggling the mechanical switch.Multiple switching ballasts may be coupled to a single mechanicalswitch, such that multiple fluorescent lamps can be turned on and offtogether in response to actuations of the single mechanical switch.

In contrast, dimming ballasts allow for control of the intensity of thecontrolled fluorescent lamp from a minimum intensity (e.g.,approximately 5%) to a maximum intensity (e.g., approximately 100%). Atypical prior art dimming ballast is operable to control the intensityof the controlled fluorescent lamp in response to a phase-controlvoltage (i.e., a dimmed-hot voltage) received from a dimmer switch. Thedimmer switch is electrically coupled between the AC power source andthe ballast (i.e., in the place of the mechanical switch that controls anon-dim ballast) and generally requires a connection to the neutral sideof the AC power source. There are typically three electrical connectionsto the prior art electronic dimming ballast: a switched-hot connection,a dimmed-hot connection, and a neutral connection. The switched-hotconnection receives a switched-hot voltage, which may be generated by arelay of the dimmer switch for turning the controlled lamp and theballast on and off. The ballast receives the phase-control voltage atthe dimmed-hot connection and is operable to determine a desiredlighting intensity in response to the length of a conduction period ofthe phase-control voltage.

It is often desirable to upgrade a non-dim ballast installation to havea dimming ballast to thus allow the user to adjust the intensity of thefluorescent lamp. In a standard non-dim installation, there is typicallyonly one electrical wire (i.e., a switched-hot voltage) coupled betweenthe electrical wallbox of the mechanical switch and the lighting fixturein which the ballast is located. Moreover, a neutral wire connectioncoupled to the neutral side of the AC power source may not be availablein the wallbox where the mechanical switch is located. However, it isdesirable to replace the non-dim ballast with the dimming ballast and toreplace the mechanical switch with the dimmer switch without running anyadditional electrical wiring between the dimmer switch and the dimmingballast (i.e., using only the pre-existing wiring). Running additionalwiring can be very expensive, due to the cost of the additionalelectrical wiring as well as the cost of installation. Typically,installing new electrical wiring requires a licensed electrician toperform the work (where simply replacing one ballast with anotherballast without running new wiring may not require a licensedelectrician). In addition, if the pre-existing wiring from themechanical switch to the ballast runs behind a fixed ceiling or wall(e.g., one comprising plaster or expensive hardwood), the electricianmay need to breach the ceiling or wall to install the new electricalwiring, which will thus require subsequent repair.

A further complication may arise when the existing ceiling containsasbestos. So long as the asbestos is not disturbed, it presents aminimal health hazard and may be left in place. However, if new wiringmust be installed between the dimmer switch and the dimming ballast,then the asbestos must be remediated. Such remediation must be performedby specially trained personnel. Also, the removed asbestos and assortedbuilding materials must be handled as hazardous waste. The process isexpensive and time consuming. Therefore, the prior art three-wiredimming ballast does not work well in retrofit installations asdescribed above because the ballast requires two electricalconnections—not one—between the dimmer switch and the ballast (i.e., theswitched-hot voltage and the dimmed-hot voltage) and the dimmer switchrequires connection to a neutral wire coupled to the neutral side of theAC power source in addition to the hot wire.

Some prior art dimming ballasts require only two connections (adimmed-hot connection for receiving the phase-control voltage and aneutral connection) and thus only a single electrical connection need bemade between the dimmer switch and the two-wire dimming ballast. Suchprior art two-wire dimming ballasts receive power (for driving thecontrolled lamp) and the phase-control voltage (for determining thedesired lighting intensity) over the single electrical connectionbetween the dimmer switch and the two-wire dimming ballasts. The desiredlighting intensity is proportional to the conduction period of thephase-control voltage. Accordingly, these two-wire ballasts may beinstalled in retrofit installations to replace non-dim ballast withoutsrunning any additional electrical wiring. A single dimmer switch maycontrol the intensities of multiple two-wire dimming ballasts coupled toreceive the phase-control voltage from the dimmer switch. However, thedimmer switch is only able to control the two-wire dimming ballasts inunison since each ballast receives the identical phase-control voltagefrom the dimmer switch. The dimmer switch cannot individually controlthe intensities of each of the ballasts coupled to the dimmer switch.Prior art two-wire ballasts are described in greater detail incommonly-assigned U.S. Pat. No. 6,111,368, issued Aug. 29, 2000,entitled SYSTEM FOR PREVENTING OSCILLATIONS IN A FLUORESCENT LAMPBALLAST, and U.S. Pat. No. 6,452,344, issued Sep. 17, 2002, entitledELECTRONIC DIMMING BALLAST, the entire disclosures of which are herebyincorporated by reference.

Some load control systems have digital electronic dimming ballasts thatallow control of individual lighting fixtures or groups of lightingfixtures independently of the electrical circuits to which the ballastsare wired for receiving power. Such load control systems typically havea controller coupled to the ballasts via a wired (low-voltage) digitalcommunication link (distinct from the power wiring) to allow for thecommunication of digital messages between the controller and theballasts. For example, the controller and ballasts may communicate usingthe industry-standard Digital Addressable Lighting Interface (DALI)communication protocol. The DALI protocol allows each DALI ballast inthe load control system to be assigned a unique digital address, to beprogrammed with configuration information (such as, for example, presetlighting intensities), and to control a fluorescent lamp in response tocommands transmitted via the communication link. Typically, a trainedinstaller is required to perform an advanced commissioning procedureusing a personal computer (PC) or other advanced programming tool toprogram the unique digital address and configuration information of theDALI ballasts.

Some DALI controllers may provide a user interface that allows forcontrol of the ballasts of the load control system. In addition, theload control system may include, for example, wall-mounted keypads orhandheld devices, such as infrared (IR) remote controls or personaldigital assistants (PDA), for controlling the electronic dimmingballasts. The IR commands are received by an IR receiving sensor thatsends appropriate commands to the controlled ballasts. In addition to IRreceiving sensors, the load control system may also include daylightsensors or occupancy sensors. The daylight and occupancy sensors monitorthe condition (e.g., the ambient light level or motion from an occupant,respectively) of a space and send appropriate commands to the controlledballasts in response to the sensed conditions in the space. Examples ofdigital electronic dimming ballasts are described in greater detail incommonly-assigned U.S. Pat. No. 7,619,539, issued Nov. 17, 2009,entitled MULTIPLE-INPUT ELECTRONIC DIMMING BALLAST WITH PROCESSOR, andU.S. Pat. No. 8,035,529, issued Oct. 11, 2011, entitled DISTRIBUTEDINTELLIGENCE BALLAST SYSTEM, the entire disclosures of which are herebyincorporated by reference.

The prior art digital dimming ballasts require that the wired digitalcommunication link is coupled to each of the ballasts—in addition to thepower wiring—and thus are not well suited to retrofit installations,where the digital dimming ballasts are replacing non-dimming ballasts.To address these limitations, some prior art control systems haveprovided for digital communication between control devices over theexisting power wiring coupled to the devices. For example, in apower-line carrier (PLC) communication system, such as an X10 controlsystem, the control devices are able to modulate high-frequency digitalmessages on the AC mains line voltage provided on the power wiring(e.g., referenced between hot and neutral of the AC power source).Examples of power-line carrier communication systems are described ingreater detail in U.S. Pat. No. 4,200,862, issued Apr. 29, 1980,entitled APPLIANCE CONTROL, and U.S. Pat. No. 4,418,333, issued Nov. 29,1983, entitled APPLIANCE CONTROL SYSTEM, the entire disclosures of whichare hereby incorporated by reference.

However, such power-line carrier communication systems have manydisadvantages that have prevented the systems from enjoying widecommercial success. Typically, the control devices of power-line carriercommunication systems require connections to both the hot side and theneutral side of the AC power source, which connections may not both beavailable in the electrical wallboxes of a retrofit installation. Inaddition, since the control devices reference the transmitted signalsbetween hot and neutral, the signals are able to travel throughout thepower system, and thus may cause noise and interference with othercontrol devices coupled to the power system. Often, such systems requireback filters to prevent the communication signals from being transmittedthroughout the power system. In addition, large reactive elements (i.e.,capacitances) coupled across the AC power source can attenuate thedigital messages transmitted by the control devices thus degrading thequality of the transmitted digital messages and decreasing thereliability of the communications of the system.

Attempts have been made to design power-line control systems that avoidthe disadvantages of the above-referenced prior art power-line carriercommunication systems. U.S. Pat. No. 5,264,823, issued Nov. 23, 1993,entitled POWER LINE COMMUNICATION SYSTEM (referred to herein as the '823patent), discloses a system in which data is transmitted on a power lineby means of momentary interruptions of the power at or near thezero-crossings of an AC waveform. The '823 patent teaches that differentpatterns of interruptions can represent different digital “words.” Theinterruptions form “notches” in an otherwise sinusoidal AC waveform. Areceiver is configured to detect the presence of the “notches,” tocompare detected patterns of “notches” with pre-stored values, and torespond if a match is found with a detected pattern.

The '823 patent proposes techniques for detecting power interruptions ator near zero-crossings, a number of which techniques are complex andsubject to error. For example, a power interruption that occurs near azero-crossing, as the '823 patent proposes, may not be reliably detecteddue to the existence of “noise” on the AC mains line. A powerinterruption that occurs away from a zero-crossing, according to the'823 patent, assertedly can be detected by “pattern recognition of somesort” or by performing “a fast Fourier transform of the waveform” andlooking for “selected high order coefficients to detect a notch.” Suchprocesses would be costly and complex to implement, and would also besusceptible to errors due to the existence of “noise” on the AC mainsline. The system disclosed in the '823 patent also has very low datatransfer rates, with at most one bit being transferred per complete ACcycle. A multi-bit message would occupy at least as many complete ACcycles in the '823 patent, and potentially twice as many cycles ifconsecutive positive half-cycles or zero-crossings were used.

U.S. Pat. No. 6,784,790, issued Aug. 31, 2004, entitledSYNCHRONIZATION/REFERENCE PULSE-BASED POWERLINE PULSE POSITION MODULATEDCOMMUNICATION SYSTEM (referred to herein as the '790 patent), disclosesa system in which control devices generate high frequency voltage pulseson the AC mains line voltage and transmit data by means of timedintervals between the pulses. In an attempt to avoid communicationerrors as a result of the attenuation of transmitted signals (which is aproblem of the prior art power-line carrier communication systems), the'790 patent proposes use of the high-frequency voltage pulses that occurnear zero-crossings and whose magnitude is much larger, relative to theAC power line voltage, than the carrier voltage pulses utilized inearlier prior art power-line carrier communication systems.

The system disclosed in the '790 patent involves superimposing a carriersignal on AC mains voltage. The transmitter in the '790 patent requiresa connection to both the hot side and the neutral side of the AC powersource and thus would not work in many retrofit situations. Thehigh-frequency voltage pulses are generated near the zero-crossings ofthe AC power source and may produce noise that could cause communicationerrors at other control devices. In addition, since the high-frequencypulses generated by the control devices of the '790 patent look verysimilar to typical noise generated by other electrical devices on the ACmains line voltage, the control devices may be susceptible tocommunication reception errors. Further, and despite their magnituderelative to AC mains voltage, the pulses proposed in the '790 patentwould be susceptible to attenuation due to large reactive elementscoupled across the AC power source.

U.S. Pat. No. 8,068,014, issued Nov. 29, 2011, entitled SYSTEM FORCONTROL OF LIGHTS AND MOTORS, discloses a system in which data istransmitted by means of a carrier signal superimposed on the loadcurrent of an isolated load control system rather than AC mains linevoltage. The system includes a transmitting device coupled in seriesbetween an AC power source and a load control device, which is coupledto an electrical load for regulating the load current conducted throughthe load. If there are multiple load control devices in acurrent-carrier communication system, the load current that is conductedby the transmitting device is divided between the multiple load controldevices. Accordingly, the magnitude of each high-frequency digitalmessage modulated onto the load current is attenuated (i.e., by currentdivision) and the quality of the digital messages may be degraded.

Despite decades of attempts to develop practical power line carrierlighting control systems, there continues to be a need for apparatusthat can reliably communicate data over a single power line between adimmer switch and an electronic dimming ballast in a low-cost lightingcontrol system. There also continues to be a need for low cost apparatusthat can reliably and selectively control a plurality of fluorescent orlight-emitting diode (LED) lighting fixtures connected to a singlecontroller by a single power line. In addition, there continues to be aneed for low cost PLC apparatus that is suitable for upgrading a simple,non-dim lighting system to a dimmed lighting system without the need foradditional wiring or a complex commissioning process.

SUMMARY OF THE INVENTION

As described herein, a load control system comprises a load controldevice for controlling an electrical load receiving power from analternating-current (AC) power source, and a controller adapted to becoupled in series electrical connection between the AC power source andthe load control device. The load control system may be installedwithout requiring any additional wires to be run. The load controldevice (i.e., a receiving device) receives both power and communicationfrom the controller (i.e., a transmitting device) over two wires (e.g.,the pre-existing wiring). The controller may be coupled to the neutralside of the AC power source (if available), but does not require aconnection to neutral.

Rather than modulating high-frequency digital messages or pulses ontothe AC mains line voltage, the controller generates a phase-controlvoltage having a variable timing edge (i.e., phase angle). Specifically,the controller transmits digital messages to the load control device bymodulating the timing edges of the phase-control voltage relative to areference edge, i.e., digital information is encoded in the timingbetween the edges. The timing of the edges of the phase-control voltagecan be controlled precisely by the controller and detected reliably bythe load control device, which does not require a zero-crossing detectorto detect the timing edges of the phase-control voltage. Since thecontroller generates a phase-control voltage for communicating digitalinformation to the load control device, the electrical hardware of thecontroller is very similar to that of a standard dimmer switch. Inaddition, the controller is able to “swallow” the phase-control signal,such that the phase-control signal only exists on the power wiringbetween the controller and the load control device, and does notgenerate noise that interferes with other control devices coupled to thepower wiring. In other words, the phase-control signal only travelsdownstream from the controller to the load control device, and notupstream from the controller to the AC power source. Since thecontroller does not modulate high-frequency digital messages onto the ACmains line voltage, large reactive elements coupled across the AC powersource do not degrade the quality of the digital messages transmitted bythe controller to the load control device.

The load control system may comprise a plurality of load control devicesthat are operable to control respective electrical loads and are coupledto the controller via a single circuit wiring. Different types of loadcontrol devices may be mixed on a single circuit and controlled by thecontroller. The load control devices may comprise, for example, adimming ballast for driving a gas-discharge lamp; a light-emitting diode(LED) driver for driving an LED light source; a dimming circuit forcontrolling the intensity of a lighting load; a screw-in luminaireincluding a dimmer circuit and an incandescent or halogen lamp; ascrew-in luminaire including a ballast and a compact fluorescent lamp; ascrew-in luminaire including an LED driver and an LED light source; anelectronic switch, controllable circuit breaker, or other switchingdevice for turning an appliance on and off; a plug-in load controldevice, controllable electrical receptacle, or controllable power stripfor controlling one or more plug-in loads; a motor control unit forcontrolling a motor load, such as a ceiling fan or an exhaust fan; adrive unit for controlling a motorized window treatment or a projectionscreen; motorized interior or exterior shutters; a thermostat for aheating and/or cooling system; a temperature control device forcontrolling a setpoint temperature of an HVAC system; an airconditioner; a compressor; an electric baseboard heater controller; acontrollable damper; a humidity control unit; a dehumidifier; a waterheater; a pool pump; a TV or computer monitor; an audio system oramplifier; a generator; an electric charger, such as an electric vehiclecharger; and an alternative energy controller.

Since the controller is operable to transmit digital messages to theload control devices via the phase-control voltage, the controller isable to control the loads individually or in groups (i.e., zones). Eachdigital message transmitted by the controller includes informationregarding a control channel (i.e., address, group, or zone information).The load control devices only respond to digital messages including thechannel to which the load control devices are assigned. The channel ofeach load control device may be set very simply using a dual inlinepackage (DIP) switch on the load control device. Accordingly, the loadcontrol system may be configured without the need for a computer or anadvanced commissioning procedure. In addition, since the load controlsystem may be installed without requiring any additional wiring and iseasily programmed, the load control system may be configured prior toshipment as a pre-programmed system that can simply be installed and isthen fully operational immediately upon first power up.

Further, the load control system may comprise a plurality ofcontrollers, each coupled to one or more load control devices via aseparate circuit wiring. In addition, the controllers may be operable totransmit digital messages to the load control devices to control theloads in response to input signals received from input devices to allowfor both local and central control of the loads. For example, thecontrollers may be operable to receive radio-frequency (RF) signals froma plurality of RF transmitters. Accordingly, the controllers may beoperable to control the electrical loads in response to the RFtransmitters in groups that are independent of the separate circuitwirings. The input devices of the load control system may comprise, forexample, occupancy sensors, vacancy sensors, daylight sensors,temperature sensors, humidity sensors, security sensors, proximitysensors, keypads, battery-powered remote controls, key fobs, cellphones, smart phones, tablets, personal digital assistants, personalcomputers, timeclocks, audio-visual controls, safety devices, centralcontrol transmitters, or any combination of these input devices.

According to an embodiment of the present invention, a load controlsystem for controlling an electrical load receiving power from an ACpower source comprises a load control device for controlling theelectrical load, and a controller adapted to be coupled in serieselectrical connection between the AC power source and the load controldevice. The controller produces a phase-control voltage that is receivedby the load control device. The controller transmits a digital messageto the load control device for controlling the load by encoding digitalinformation in timing edges of the phase-control voltage. Thephase-control voltage has at least one timing edge in each half-cycle ofthe AC power source when the controller is transmitting the digitalmessage to the load control device.

According to another embodiment of the present invention, a controllerfor controlling the power delivered from an AC power source to anelectrical load by a load control device comprises a controllablyconductive device adapted to be coupled in series electrical connectionbetween the AC power source and the load control device, and a controlcircuit coupled to the controllably conductive device for rendering thecontrollably conductive device conductive each half-cycle of the ACpower source to generate a phase-control voltage. The control circuitrenders the controllably conductive device conductive for a portion ofeach half-cycle of the AC power source. The control circuit transmits adigital message to the load control device for controlling the powerdelivered to the load by encoding digital information in timing edges ofthe phase-control voltage. The phase-control voltage has at least onetiming edge in each half-cycle of the AC power source when the controlcircuit is transmitting the digital message to the load control device.

According to another embodiment of the present invention, a load controldevice for controlling the power delivered from an AC power source to anelectrical load in response to a controller comprises a load regulationcircuit adapted to be coupled to the electrical load for controlling thepower delivered to the load, and a control circuit coupled to the loadregulation circuit for controlling the power delivered to the load inresponse to a phase-control voltage received from the controller. Thecontrol circuit is operable to control the power delivered to the loadin response to digital information encoded in timing edges of thephase-control voltage. The phase-control voltage received from thecontroller has at least one timing edge in each half-cycle of the ACpower source when the digital information is encoded in the timing edgesof the phase-control voltage.

In addition, a retrofit kit comprises a load control device adapted tocontrol the power delivered from an AC power source to an electricalload in response to a controller, where the load control device isoperable to receive a phase-control voltage and to control the powerdelivered to the load in response to digital information encoded in thetiming edges of the phase-control voltage. The phase-control voltagereceived from the controller has at least one timing edge in eachhalf-cycle of the AC power source when the digital information isencoded in the timing edges of the phase-control voltage.

Further, a method of transmitting a digital message from a controller toa load control device for controlling an electrical load receiving powerfrom an AC power source is presented herein. The method comprises: (1)the controller generating a phase-control voltage; (2) the controllertransmitting a digital message by encoding digital information in thetiming edges of the phase-control voltage, the phase-control voltagehaving at least one timing edge in each half-cycle of the AC powersource when the controller is transmitting the digital message; (3) theload control device receiving the phase-control voltage from thecontroller; and (4) the load control device controlling the load inresponse to the digital information encoded in the timing edges of thephase-control voltage.

According to another aspect of the present invention, a load controlsystem comprises a load control device adapted to be coupled to anelectrical load for controlling the power delivered to the electricalload from an AC power source, and a controller adapted to be coupled inseries electrical connection between the AC power source and the loadcontrol device and operable to produce a phase-control voltage that isadapted to be received by the load control device. The phase-controlvoltage produced by the controller is characterized by a number ofsequential data patterns. Each data pattern has a first timing edge at apredetermined reference edge time during a first half-cycle and a secondtiming edge at a data edge time during a second subsequent half-cycle,such that an offset time period exists between the reference edge timeand the data edge time of each data pattern. The load control devicereceives the phase-control voltage from the controller, and thecontroller transmits a digital message to the load control device forcontrolling the power delivered to the load by controlling the offsettime period in each of the sequential data patterns.

According to another embodiment of the present invention, a controllerfor controlling the power delivered from an AC power source to anelectrical load by a load control device comprises a controllablyconductive device adapted to be coupled in series electrical connectionbetween the source and the load control device, and a control circuitcoupled to the controllably conductive device for rendering thecontrollably conductive device conductive each half-cycle of the ACpower source to generate a phase-control voltage having a number ofsequential data patterns. Each data pattern has a first timing edge at apredetermined reference edge time during a first half-cycle and a secondtiming edge at a data edge time during a second subsequent half-cycle,such that an offset time period exists between the reference edge timeand the data edge time of each data pattern. The control circuittransmits a digital message to the load control device for controllingthe power delivered to the load by controlling the offset time period ineach of the sequential data patterns.

According to another embodiment of the present invention, a load controldevice comprises a load regulation circuit adapted to be coupled to anelectrical load, and a control circuit coupled to the load regulationcircuit for controlling the power delivered to the load from an AC powersource in response to a phase-control voltage received from acontroller. The control circuit detects a number of sequential datapatterns of the phase-control voltage, where each data pattern has afirst timing edge at a reference edge time during a first half-cycle anda second timing edge at a data edge time during a second subsequenthalf-cycle. The control circuit measures an offset time period betweenthe reference edge time and the data edge time of each data pattern,decodes a digital message from the controller based on the measuredoffset time periods in each of the sequential data patterns, andcontrols the power delivered to the load in response to the digitalmessage.

In addition, a method of transmitting a digital message from acontroller to a load control device for controlling an electrical loadreceiving power from an AC power source is also described herein. Themethod comprises: (1) the controller generating a phase-control voltagehaving a number of sequential data patterns, each data pattern having afirst timing edge at a predetermined reference edge time during a firsthalf-cycle and a second timing edge at a data edge time during a secondsubsequent half-cycle, such that an offset time period exists betweenthe reference edge time and the data edge time of each data pattern; (2)the controller transmitting a digital message by controlling the offsettime period in each of the sequential data patterns; (3) the loadcontrol device receiving the phase-control voltage from the controller;(4) the load control device decoding the digital message based on theoffset time periods of the phase-control voltage; and (5) the loadcontrol device controlling the load in response to the digital messagereceived from the controller.

According to another aspect of the present invention, a load controlsystem for controlling a plurality of electrical loads receiving powerfrom an AC power source via a power wiring comprises a plurality of loadcontrol devices adapted to be coupled in parallel with each other andoperable to control respective electrical loads, and a control circuitadapted to be coupled in series electrical connection between the ACpower source and the parallel combination of the load control devicesvia the power wiring. The control circuit produces a phase-controlvoltage that is received by the load control devices and transmits adigital message to the load control devices via the power wiring byencoding digital information in the timing edges of the phase-controlvoltage. The phase-control voltage has at least one timing edge in eachhalf-cycle of the AC power source when the controller is transmittingthe digital message to the load control devices. The digital messageincludes data representing at least one of a plurality of controlchannels, which indicates which of the load control devices should reactto the digital message.

According to another aspect of the present invention, a load controlsystem for controlling a plurality of electrical loads receiving powerfrom an AC power source via a power wiring comprises a plurality of loadcontrol devices adapted to be coupled in parallel with each other andoperable to control respective electrical loads, and a control circuitadapted to be coupled in series electrical connection between the ACpower source and the parallel combination of the load control devicesvia the power wiring. The control circuit produces a phase-controlvoltage that is adapted to be received by the load control devices andis characterized by a number of sequential data patterns. Each datapattern has a first timing edge at a predetermined reference edge timeduring a first half-cycle and a second timing edge at a data edge timeduring a second subsequent half-cycle, such that an offset time periodexists between the reference edge time and the data edge time of eachdata pattern. The control circuit transmits a digital message to theload control devices via the power wiring by controlling the offset timeperiod in each of the sequential data patterns. The digital messageincludes data representing at least one of a plurality of controlchannels, which indicates which of the load control devices should reactto the digital message.

According to another aspect of the present invention, a load controlsystem comprises a load control device for controlling an electricalload receiving power from an AC power source via a power wiring, acontroller adapted to be coupled in series electrical connection betweenthe AC power source and the load control device, and an input deviceoperable to transmit a control signal to the controller. The controllerproduces a phase-control voltage, which is received by the load controldevice. The controller transmits a digital message to the electricalload control device for controlling the load by encoding digitalinformation in timing edges of the phase-control voltage in response tothe control signal received from the input device.

According to another embodiment of the present invention, a controllerfor controlling the power delivered from an AC power source to anelectrical load by a load control device comprises a controllablyconductive device adapted to be coupled in series electrical connectionbetween the source and the load control device, a control circuitcoupled to the controllably conductive device for rendering thecontrollably conductive device conductive for a portion of eachhalf-cycle of the AC power source to generate a phase-control voltage,and an input circuit coupled to the control circuit for receiving acontrol signal from an input device. The control circuit transmits adigital message to the load control device for controlling the powerdelivered to the load by encoding digital information in timing edges ofthe phase-control voltage in response to the received control signal.

In addition, a method of transmitting a digital message from acontroller to a load control device for controlling an electrical loadreceiving power from an AC power source is also described herein. Themethod comprises: (1) transmitting an RF signal to the controller froman RF transmitter; (2) the controller generating a phase-control voltagehaving at least one timing edge in each half-cycle of the AC powersource; (3) the controller transmitting a digital message by encodingdigital information in timing edges of the phase-control voltage inresponse to the RF signal received from the RF transmitter; (4) the loadcontrol device receiving the phase-control voltage from the controller;and (5) the load control device controlling the load in response to thedigital information encoded in the timing edges of the phase-controlvoltage.

According to another aspect of the present invention, a load controlsystem for controlling a plurality of electrical loads receiving powerfrom an AC power source via a power wiring comprises a plurality of loadcontrol devices adapted to be coupled in parallel with each other andoperable to control respective electrical loads, a controller adapted tobe coupled in series electrical connection between the AC power sourceand the parallel combination of the load control devices via the powerwiring, and a plurality of input devices operable to transmit controlsignals to the controller. The controller produces a phase-controlvoltage that is received by the load control device. The controllertransmits a digital message to the load control device via the powerwiring by encoding digital information in timing edges of thephase-control voltage in response to a control signal received from oneof the input devices. The digital message includes data representing atleast one of a plurality of control channels that is dependent upon theinput device from which the control signal was received.

According to another aspect of the present invention, a load controlsystem for controlling an electrical load receiving power from an ACpower source via a power wiring comprises a load control device forcontrolling the electrical load, and a controller operable to produce aphase-control voltage and swallow the phase-control signal, such thatthe phase-control signal only exists on the power wiring between thecontroller and the load control device. The controller comprises acontrollably conductive device adapted to be coupled in serieselectrical connection between the AC power source and the load controldevice via the power wiring, such that the controllably conductivedevice is operable to conduct a load current from the AC power source tothe electrical load. The controller transmits a digital message to theload control device for controlling the load by encoding digitalinformation in timing edges of the phase-control voltage.

According to another embodiment of the present invention, a controllerfor controlling the power delivered from an AC power source to anelectrical load by a load control device comprises: (1) a hot terminaladapted to be coupled to the AC power source; (2) a control-hot terminaladapted to be coupled to the load control device; (3) a controllablyconductive device coupled between the hot terminal and the control-hotterminal, such that the controllably conductive device is adapted to becoupled in series electrical connection between the AC power source andthe load control device, so as to conduct a load current from the ACpower source to the load control device; and (4) a control circuitcoupled to the controllably conductive device for rendering thecontrollably conductive device conductive for a portion of eachhalf-cycle of the AC power source to generate a phase-control voltagethat only exists at the control-hot terminal. The control circuittransmits a digital message to the load control device for controllingthe power delivered to the load by encoding digital information intiming edges of the phase-control voltage.

According to another aspect of the present invention, a load controlsystem for controlling the power delivered to a plurality of electricalloads comprises a plurality of load control devices, a plurality ofcontrollers, and an input device. Each of the load control devices isadapted to be coupled to one or more of the electrical loads forcontrolling the power delivered to the loads. The plurality of loadcontrol devices comprises a first load control device and a second loadcontrol device coupled in parallel electrical connection, and a thirdload control device and a fourth load control device coupled in parallelelectrical connection. The first and second load control devices arecoupled to a first circuit wiring for receiving power from an AC powersource, while the third and fourth load control devices are coupled to asecond circuit wiring for receiving power from the AC power source. Theplurality of controllers comprises a first controller coupled to thefirst circuit wiring in series electrical connection between the ACpower source and the first and second load control devices, and a secondcontroller coupled to the second circuit wiring in series electricalconnection between the AC power source and the third and fourth loadcontrol devices. The first and third load control devices arecharacterized with a first channel, while the second and fourth loadcontrol devices are characterized with a second channel. The inputdevice is adapted to transmit control signals directly to the first andsecond controllers. The first controller transmits a first digitalmessage to the first and second load control devices via the firstcircuit wiring and the second controller transmits a second digitalmessage to the third and fourth load control devices via the secondcircuit wiring in response to the control signals received from theinput device. The first and second digital messages each indicate thefirst channel, such that the first and third load control devices areresponsive to the first and second digital messages transmitted by thefirst and second controllers in response to the control signals receivedfrom the input device.

According to another embodiment of the present invention, a lightingcontrol system for controlling the intensities of a plurality offluorescent lamps comprises a plurality of two-wire digital ballasts, aplurality of ballast controllers, and a wireless transmitter. Each ofthe ballasts is adapted to be coupled to one or more of the plurality oflamps for controlling the intensities of the lamps. The plurality ofballasts comprises a first ballast and a second ballast coupled inparallel electrical connection, and a third ballast and a fourth ballastcoupled in parallel electrical connection. The first and second ballastsare coupled to a first circuit wiring for receiving power from an ACpower source, while the third and fourth ballasts are coupled to asecond circuit wiring for receiving power from the AC power source. Theplurality of ballast controllers comprises a first ballast controllercoupled to the first circuit wiring in series electrical connectionbetween the AC power source and the first and second ballasts, and asecond ballast controller coupled to the second circuit wiring in serieselectrical connection between the AC power source and the third andfourth ballasts. The first and third ballasts are characterized with afirst channel and the second and fourth ballasts are characterized witha second channel. The wireless transmitter is adapted to transmitwireless signals directly to the first and second ballast controllers.The first ballast controller transmits a first digital message to thefirst and second ballasts via the first circuit wiring and the secondballast controller transmits a second digital message to the third andfourth ballasts via the second circuit wiring in response to thewireless signals received from the wireless transmitter. The first andsecond digital messages indicate the first channel, such that the firstand third ballasts are responsive to the digital messages transmitted inresponse to the wireless signals transmitted by the wirelesstransmitter.

According to another aspect of the present invention, a load controlsystem comprises a load control device adapted to be coupled to anelectrical load for controlling the power delivered to the electricalload from an AC power source, and a controller adapted to be coupled inseries electrical connection between the AC power source and the loadcontrol device, and operable to produce a phase-control voltage that isreceived by the load control device. The controller transmits digitalmessages to the load control device for controlling the power deliveredto the load by encoding digital information in timing edges of thephase-control voltage. The controller is operable to interrupt a firstdigital message that is being transmitted in order to transmit a seconddigital message to the load control device.

According to another embodiment of the present invention, a controllerfor controlling the power delivered from an AC power source to anelectrical load by a load control device comprises a controllablyconductive device adapted to be coupled in series electrical connectionbetween the source and the load control device, and a control circuitcoupled to the controllably conductive device for rendering thecontrollably conductive device conductive for a portion of eachhalf-cycle of the AC power source to generate a phase-control voltage.The control circuit transmits digital messages to the load controldevice for controlling the power delivered to the load by encodingdigital information in timing edges of the phase-control voltage, and isoperable to interrupt a first digital message that is being transmittedin order to transmit a second digital message to the load controldevice.

According to another embodiment of the present invention, a load controldevice comprises a load regulation circuit adapted to be coupled to anelectrical load for controlling the power delivered to the load from anAC power source, and a control circuit coupled to the load regulationcircuit for controlling the power delivered to the load in response todigital information encoded in timing edges of a phase-control voltagereceived from a controller. The control circuit is operable to begindecoding a first digital message from the controller, determine that asecond digital message is being transmitted before the end of the firstdigital message, and begin decoding the second digital message insteadof decoding the first digital message.

In addition, a method of transmitting a digital message from acontroller to a load control device for controlling an electrical loadreceiving power from an AC power source is also described herein. Themethod comprises: (1) the controller generating a phase-control voltage;(2) the controller transmitting a first digital message to thecontroller by encoding digital information in timing edges of thephase-control voltage; (3) the load control device receiving thephase-control voltage from the controller; (4) the controllerinterrupting the first digital message that is being transmitted inorder to transmit a second digital message to the load control devices;and (5) the load control device controlling the load in response to thesecond digital message received from the controller via thephase-control voltage.

According to another aspect of the present invention, a controller forcontrolling the power delivered from an AC power source to a lightingload is operable to alternately operate in a dimmer mode and a digitalcommunication mode. The controller comprises a controllably conductivedevice adapted to be coupled in series electrical connection between theAC power source and the lighting load, and a control circuit coupled tothe controllably conductive device for rendering the controllablyconductive device conductive for a portion of each half-cycle of the ACpower source for generating a phase-control voltage to control theintensity of lighting load. When operating in the dimmer mode, thecontrol circuit renders the controllably conductive device conductiveeach half-cycle at a phase angle that is dependent upon the desiredlighting intensity. When operating in the digital communication mode,the control circuit transmits digital messages by encoding digitalinformation for controlling the intensity of the lighting load in timingedges of the phase-control voltage.

According to another embodiment of the present invention, a load controldevice for controlling the power delivered from an AC power source to alighting load in response to a controller comprises a load regulationcircuit adapted to be coupled to the electrical load for controlling thepower delivered to the lighting load and thus the intensity of thelighting load, and a control circuit coupled to the load regulationcircuit for controlling the intensity of the lighting load in responseto a phase-control voltage received from the controller and operable toalternately operate in a dimmer mode and a digital communication mode.The control circuit controls the intensity of the lighting load independence upon a phase angle of the phase-control voltage whenoperating in the dimmer mode and in response to digital informationencoded in timing edges of the phase-control voltage when operating inthe digital communication mode.

According to another embodiment of the present invention, a load controlsystem for controlling an electrical load receiving power from an ACpower source comprises a load control device for controlling theelectrical load, and a controller adapted to be coupled in serieselectrical connection between the AC power source and the load controldevice, and to produce a phase-control voltage having timing edgesduring consecutive half-cycles of the AC power source. The load controldevice receives the phase-control voltage from the controller, and thecontroller transmits digital messages to the load control device forcontrolling the load by adjusting the times of the timing edges duringthe consecutive half-cycles.

In addition, a system for encoding digital data in an alternatingcurrent powering a controlled device over an alternating currentelectrical network is also presented herein. The digital data controls aprocessor of the controlled device. The system comprises a controlcircuit having a controlled switch disposed in series between a sourceof the alternating current and the controlled device and passing thealternating current to the controlled device over the electricalnetwork. The controlled switch has a control input responsive to aninput signal. The control circuit encodes control information in thealternating current passed to the controlled device by the controlledswitch from which the processor can decode the digital data to controlthe controlled device. The control circuit causes the controlled switchto make a first transition in said alternating current in a firsthalf-cycle of the alternating current and to make a second transition ina second half-cycle of said alternating current, with a time differencebetween the two transitions defining the digital data.

According to another embodiment of the present invention, a method forencoding digital data in an alternating current powering a controlleddevice over an alternating current electrical network, wherein thedigital data controls a processor of the controlled device, comprises:(1) providing a control circuit having a controlled switch disposed inseries between a source of the alternating current and the controlleddevice and passing the alternating current to the controlled device overthe electrical network; and (2) providing a control signal to a controlinput of the controlled switch to encode control information in thealternating current passed to the controlled device from which theprocessor can decode the digital data to control the controlled device,the control signal causing the controlled switch to make a firsttransition in said alternating current in a first half-cycle of thealternating current and to make a second transition in a secondhalf-cycle of said alternating current, with a time difference betweenthe two transitions defining the digital data.

According to another embodiment of the present invention, a system forcommunication over an AC electrical power network comprises at least onecontrolled device, and a control circuit coupled to the electrical powernetwork to provide electrical power to the at least one controlleddevice. The control circuit comprises an input connection coupled toreceive AC electrical power from the electrical power network, an outputconnection coupled to provide an output AC power signal to the at leastone controlled device to provide electrical power to the controlleddevice and to provide data communication with the at least onecontrolled device, a controlled switch for switching the AC electricalpower from the input connection to the output connection to provide theoutput AC power signal to the controlled device, and a control input forreceiving a control signal controlling the controlled switch to providethe output AC power signal to the controlled device to power thecontrolled device. The output AC power signal is modified in response tothe control input by the controlled switch to change a phase angle atwhich the controlled switch makes a transition between on and off or offand on to one of a plurality of phase angles of the AC electrical powersignal to thus encode the information in the control signal in theplurality of phase angles of the output AC power signal and control afunction of the controlled device. The controlled device comprises aprocessor for deriving digital data from the encoded information in theoutput AC power signal to control the controlled device.

Further, an apparatus for communication over an AC electrical powernetwork is also described herein. The apparatus comprises a controlcircuit coupled to the electrical power network to provide electricalpower to at least one controlled device. The control circuit comprisesan input connection coupled to receive AC electrical power from theelectrical power network and an output connection coupled to provide anoutput AC power signal to the at least one controlled device to provideelectrical power to the controlled device and to provide datacommunication with the at least one controlled device. The controlcircuit further comprises a controlled switch for switching the ACelectrical power from the input connection to the output connection toprovide the output AC power signal to the controlled device, and acontrol input for receiving a control signal controlling the controlledswitch to provide the output AC power signal to the controlled device topower the controlled device. The controlled switch is controlled inresponse to the control input to encode information in the controlsignal in cycles of the output AC power signal as sequential phasecontrolled signals to control a function of the controlled device.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail in the followingdetailed description with reference to the drawings in which:

FIG. 1 is a simple wiring diagram of a lighting control system having aplurality of two-wire digital dimming ballasts and a digital ballastcontroller according to a first embodiment of the present invention;

FIG. 2A shows example input devices of the load control system of FIG.1;

FIG. 2B shows example form factors of the digital ballast controller ofthe load control system of FIG. 1;

FIG. 2C shows example electrical load and load control devices of theload control system of FIG. 1;

FIG. 3A is a simplified block diagram of the digital ballast controllerof FIG. 1;

FIG. 3B is a simplified block diagram of the digital dimming ballast ofFIG. 1;

FIGS. 4A and 4B are floor plan diagrams of example installations of thelighting control system of FIG. 1 in a classroom;

FIG. 5 is a simplified perspective view of a retrofit kit having thedigital dimming ballasts of FIG. 3B pre-wired to lamp sockets andmounted to a pan;

FIG. 6 is a simple timing diagram of a control-hot voltage generated bythe digital ballast controller for communicating digital messages withthe digital dimming ballasts of the lighting control system of FIG. 1according to the first embodiment of the present invention;

FIG. 7 is a simple diagram of a message structure for the digitalmessages transmitted by the digital ballast controller to the digitaldimming ballasts of the lighting control system of FIG. 1;

FIG. 8 is a simple timing diagram of the control-hot voltage showing astart pattern including a unique start symbol generated by the digitalballast controller for starting the digital messages transmitted to thedigital dimming ballasts of the lighting control system of FIG. 1according to the first embodiment of the present invention;

FIG. 9 is a simplified flowchart of a button procedure executed by amicroprocessor of the digital ballast controller of FIG. 2 in responseto an actuation of an actuator of the digital ballast controller;

FIGS. 10A and 10B are simplified flowcharts of an RF message procedureexecuted by the microprocessor of the digital ballast controller of FIG.2 when a digital message is received from an RF transmitter of thelighting control system of FIG. 1;

FIG. 11 is a simplified flowchart of a zero-crossing procedure executedby the microprocessor of the digital ballast controller of FIG. 2;

FIG. 12 is a simplified flowchart of a timer interrupt procedureexecuted by the microprocessor of the digital ballast controller of FIG.2;

FIG. 13 is a simplified flowchart of a data edge procedure executed bythe microprocessor of the digital ballast controller of FIG. 2;

FIG. 14 is a simplified flowchart of a receiving procedure executed by amicroprocessor of each of the digital dimming ballasts of the lightingcontrol system of FIG. 1 each half-cycle to receive the digital messagestransmitted by the digital ballast controller;

FIG. 15 is a simplified flowchart of the receive data procedure executedby the microprocessor of each digital dimming ballast of lightingcontrol system of FIG. 1 to determine the bits of data of the receiveddigital messages;

FIG. 16 is a simple timing diagram of a control-hot voltage according tothe second embodiment of the present invention;

FIG. 17 is a simple timing diagram of the control-hot voltage showingthe start pattern according to the second embodiment of the presentinvention;

FIG. 18 is a simplified flowchart of a timer interrupt procedureexecuted by the microprocessor of each digital ballast controller togenerate the reference and data edges of the transmitted digitalmessages according to the second embodiment of the present invention;

FIG. 19 is a simplified flowchart of a receiving procedure executed bythe microprocessor of each digital dimming ballast periodically toreceive the digital messages from the digital ballast controlleraccording to the second embodiment of the present invention;

FIG. 20 is a simplified block diagram of a lighting control systemcomprising a two-wire digital ballast controller that does not require aneutral connection and an active load circuit according to a thirdembodiment of the present invention;

FIG. 21 is a simplified block diagram of the digital ballast controllerand the active load circuit of the lighting control system of FIG. 20according to the third embodiment of the present invention;

FIG. 22 is a simplified block diagram of a lighting control systemcomprising a digital dimming ballast that is directly connected to oneor more input devices according to a fourth embodiment of the presentinvention; and

FIG. 23 is a simple wiring diagram of a lighting control system having aplurality of two-wire LED drivers and a digital LED controller accordingto a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 1 is a simple wiring diagram of a load control system 100 having aplurality of two-wire load control devices, such as two-wire digitaldimming ballasts 110, according to a first embodiment of the presentinvention. The two-wire digital dimming ballasts 110 are coupled torespective lamps 104 for controlling the intensities of the lamps to adesired lighting intensity L_(DES) between a low-end (i.e., minimum)intensity L_(LE) (e.g., approximately 1%) and a high-end (i.e., maximum)intensity L_(HE) (e.g., approximately 100%). The load control system 100also comprises a digital ballast controller 120 (i.e., a remote controldevice) that is adapted to be coupled in series electrical connectionbetween an alternating-current (AC) power source 102 and the two-wiredigital dimming ballasts 110 via a circuit wiring 114. In other words,each digital dimming ballast 110 is coupled in series with the digitalballast controller 120 across the AC power source 102. As shown in FIG.1, the digital ballast controller 120 may be directly coupled to theneutral side of the AC power source 102. The circuit wiring 114 may bethe pre-existing wiring of the electrical network of the building inwhich the load control system 100 is installed and may be located in theinterior and exterior of the building.

The two-wire digital dimming ballasts 110 are coupled in parallel andreceive both power and digital communication from a control-hot voltageV_(CH) (i.e., a phase-control voltage) that is generated by the digitalballast controller 120 as will be described in greater detail below. Thecontrol-hot voltage V_(CH) generated by the digital ballast controller120 differs from the phase-control voltage received by prior artthree-wire and two-wire dimming ballasts in that the digital dimmingballasts 110 of the load control system 100 do not determine the desiredlighting intensity L_(DES) for the respective lamp 104 in response tothe length of the conduction period of the control-hot voltage V_(CH).Rather, the two-wire digital dimming ballasts 110 of the load controlsystem 100 are able to determine the desired lighting intensity L_(DES)(i.e., are controlled to a defined state) in response to the digitalcontrol information (i.e., digital communication messages) derived fromthe control-hot voltage V_(CH).

As shown in FIG. 1, the digital ballast controller 120 may be a wallboxdevice, i.e., adapted to be wall-mounted in a standard single-gangelectrical wallbox, thus replacing a standard mechanical switch that mayhave been controlling the power delivered to the ballasts 110 prior toinstallation of the digital ballast controller. The digital ballastcontroller 120 comprises a faceplate 122 and a user interface that isreceived in an opening of the faceplate and includes a toggle actuator124 and an intensity adjustment actuator 126 for receiving user inputsto control the fluorescent lamps 104. The digital ballast controller 120communicates with the digital dimming ballasts 110 to cause thefluorescent lamps 104 to toggle, i.e., turn off and on, in response toactuations of the toggle actuator 124. The digital ballast controller120 increases and decreases the lighting intensity of the fluorescentlamps 104 in response to actuations of an upper portion 126A or a lowerportion 126B of the intensity adjustment actuator 126, respectively. Theuser interface of the digital ballast controller 120 also includes aplurality of visual indicators 128, e.g., light-emitting diodes (LEDs),which are arranged in a linear array and are illuminated to providefeedback of the intensity of the fluorescent lamps 104.

The load control system 100 may also comprise a plurality of inputdevices, for example, wireless transmitters, such as a wirelessoccupancy sensor 130, a wireless daylight sensor 140, and a wirelessbattery-powered remote control 150, which are operable to transmitdigital messages (i.e., input signals) to the digital ballast controller120 via radio-frequency (RF) signals 106. The digital ballast controller120 is operable to turn the fluorescent lamps 104 on and off and adjustthe intensities of the fluorescent lamps 104 in response to the digitalmessages received from the occupancy sensor 130, the daylight sensor140, and the battery-powered remote control 150. The wirelesstransmitters may be operable to transmit the digital messages to thedigital ballast controller 120 according to a predefined RFcommunication protocol, such as, for example, one of LUTRON CLEARCONNECT, WIFI, ZIGBEE, Z-WAVE, KNX-RF, and ENOCEAN RADIO protocols.Alternatively, the wireless transmitters could transmit the digitalmessages via a different wireless medium, such as, for example, infrared(IR) signals or sound (such as voice). The digital ballast controller120 may be operable to transmit digital messages to the digital dimmingballasts 110 via the control-hot voltage V_(CH) in response to receivingRF signals from via a wireless network (i.e., via the Internet).

Because the digital dimming ballasts 110 are typically mounted insidemetal lighting fixtures, the digital dimming ballasts 110 are typicallynot able to receive the RF signals 106 from the wireless transmitters.However, since the digital ballast controller 120 transmits digitalmessages to the digital dimming ballasts 110 via the control-hot voltageV_(CH) in response to receiving the RF signals 106 from the wirelesstransmitters, the fluorescent lamps 104 are able to be controlled inresponse to the wireless transmitters.

During a setup procedure of the load control system 100, the digitalballast controller 120 is associated with the occupancy sensor 130, thedaylight sensor 140, and the battery-powered remote control 150, forexample, by pressing an actuator on the wireless transmitter andpressing an actuator on the digital ballast controller (e.g., the toggleactuator 124). All digital messages transmitted to the digital ballastcontroller 120 by the occupancy sensor 130, the daylight sensor 140, andthe battery-powered remote control 150 may include a command andidentifying information, for example, a serial number (i.e., a uniqueidentifier) associated with the wireless transmitter. The digitalballast controller 120 is responsive to messages containing the serialnumbers of the occupancy sensor 130, the daylight sensor 140, and thebattery-powered remote control 150 to which the digital ballastcontroller is associated.

The occupancy sensor 130 may be removably mountable to a ceiling (asshown in FIG. 1) or to a wall, for example, in the vicinity of (i.e., aspace around) the fluorescent lamps 104 controlled by the ballasts 110.The occupancy sensor 130 is operable to detect occupancy conditions inthe vicinity of the fluorescent lamps, and includes an internaldetector, e.g., a pyroelectric infrared (PIR) detector, which is housedin an enclosure 132 having a lens 134. The internal detector is operableto receive infrared energy from an occupant in the space via the lens134 to thus sense the occupancy condition in the space. The occupancysensor 130 is operable to process the output of the PIR detector todetermine whether an occupancy condition (i.e., the presence of theoccupant) or a vacancy condition (i.e., the absence of the occupant) ispresently occurring in the space, for example, by comparing the outputof the PIR detector to a predetermined occupancy voltage threshold.Alternatively, the internal detector could comprise an ultrasonicdetector, a microwave detector, or any combination of PIR detectors,ultrasonic detectors, and microwave detectors.

The occupancy sensor 130 operates in an “occupied” state or a “vacant”state in response to the detections of occupancy or vacancy conditions,respectively, in the space. If the occupancy sensor 130 is in the vacantstate and the occupancy sensor determines that the space is occupied inresponse to the PIR detector, the occupancy sensor changes to theoccupied state. The occupancy sensor 130 transmits digital messageswirelessly via RF signals 106 to the digital ballast controller 120 inresponse to the present state of the occupancy sensor. The commandsincluded in the digital messages transmitted to the digital ballastcontroller 120 by the occupancy sensor 130 may comprise an occupiedcommand or a vacant command.

When the fluorescent lamps 104 are off, the digital ballast controller120 is operable to turn on the fluorescent lamps in response toreceiving the occupied command from the occupancy sensor 130. Thedigital ballast controller 120 is operable to turn off the fluorescentlamps 104 in response to receiving the vacant command from the occupancysensor 130. If there were more than one occupancy sensor 120 in the loadcontrol system 100, the digital ballast controller 120 would turn on thefluorescent lamps 104 in response to receiving a first occupied commandfrom any one of the occupancy sensors, and turn off the fluorescentlamps in response to the last vacant command received from thoseoccupancy sensors from which the occupancy sensor received occupiedcommands. For example, if two occupancy sensors 130 both transmitoccupied commands to the digital ballast controller 120, the digitalballast controller will not turn off the fluorescent lamps 104 untilsubsequent vacant commands are received from both of the occupancysensors. Accordingly, the occupancy sensor 130 provides automaticcontrol and energy savings by turning off the fluorescent lamps 104 whenthe space is unoccupied.

Alternatively, the occupancy sensor 130 could be implemented as avacancy sensor. The digital ballast controller 120 would only operate toturn off the fluorescent lamps 104 in response to receiving the vacantcommands from the vacancy sensor. Therefore, if the load control system100 includes vacancy sensors, the fluorescent lamps 104 must be turnedon manually (e.g., in response to a manual actuation of the toggleactuator 124 of the digital ballast controller 120). Examples of RF loadcontrol systems having occupancy and vacancy sensors are described ingreater detail in commonly-assigned U.S. patent application Ser. No.12/203,518, filed Sep. 3, 2008, entitled RADIO-FREQUENCY LIGHTINGCONTROL SYSTEM WITH OCCUPANCY SENSING; U.S. patent application Ser. No.12/203,500, filed Sep. 3, 2008, entitled BATTERY-POWERED OCCUPANCYSENSOR; and U.S. patent application Ser. No. 12/371,027, filed Feb. 13,2009, entitled METHOD AND APPARATUS FOR CONFIGURING A WIRELESS SENSOR,the entire disclosures of which are hereby incorporated by reference.

The daylight sensor 140 is mounted so as to measure a total lightintensity in the space around the daylight sensor (i.e., in the vicinityof the fluorescent lamps 104). The daylight sensor 140 includes aninternal photosensitive circuit, e.g., a photosensitive diode, which ishoused in an enclosure 142 having a lens 144 for conducting light fromoutside the daylight sensor towards the internal photosensitive diode.The daylight sensor 140 is responsive to the total light intensitymeasured by the internal photosensitive circuit. Specifically, thedaylight sensor 140 is operable to wirelessly transmit digital messagesincluding a value representative of the total light intensity to thedigital ballast controller 120 via the RF signals 106. The digitalballast controller 120 automatically adjusts the lighting intensities ofthe fluorescent lamps 104 in response to the total light intensitymeasured by the daylight sensor 140, so as to reduce the total powerconsumed by the load control system 100. If there is more than onedaylight sensor 140 in the load control system 100, the digital ballastcontroller 120 may be operable to, for example, average the values ofthe total light intensities measured by multiple daylight sensors 140and then adjust the intensities of the fluorescent lamps 104 in responseto the average of the values of the total light intensities measured bymultiple daylight sensors. Examples of RF load control systems havingdaylight sensors are described in greater detail in commonly-assignedU.S. patent application Ser. No. 12/727,956, filed Mar. 19, 2010,entitled WIRELESS BATTERY-POWERED DAYLIGHT SENSOR, and U.S. patentapplication Ser. No. 12/727,923, filed Mar. 19, 2010, entitled METHOD OFCALIBRATING A DAYLIGHT SENSOR, the entire disclosures of which arehereby incorporated by reference.

The battery-powered remote control 150 comprises an on button 152, anoff button 154, a raise button 155, a lower button 156, and a presetbutton 158 for providing manual control of the fluorescent lamps 104 bya user of the load control system 100. The remote control 150 isoperable to transmit digital messages including commands to control thefluorescent lamps 104 to the digital ballast controller 120 in responseto actuations of the buttons 152-158. Specifically, the battery-poweredremote control 150 simply transmits information regarding which of thebuttons 152-158 was actuated to the digital ballast controller 120 viathe RF signals 106. The digital ballast controller 120 turns thefluorescent lamps 104 on and off in response to actuations of the onbutton 152 and the off button 154 of the remote control 150,respectively. The digital ballast controller 120 raises and lowers theintensity of the fluorescent lamps 104 in response to actuations of theraise button 155 and the lower button 156, respectively. The digitalballast controller 120 controls the intensity of each of the fluorescentlamps 104 to a preset intensity in response to actuations of the presetbutton 158. Examples of battery-powered remote controls are described ingreater detail in commonly-assigned U.S. patent application Ser. No.12/399,126, filed Mar. 6, 2009, entitled WIRELESS BATTERY-POWERED REMOTECONTROL HAVING MULTIPLE MOUNTING MEANS, and U.S. Pat. No. 7,573,208,issued Aug. 22, 1009, entitled METHOD OF PROGRAMMING A LIGHTING PRESETFROM A RADIO-FREQUENCY REMOTE CONTROL the entire disclosures of whichare hereby incorporated by reference.

The load control system 100 may comprise a plurality of occupancysensors 130, daylight sensors 140, and battery-powered remote controls150 for providing local control of the fluorescent lamps 104. Inaddition, the load control system 100 may comprise additional types ofinput devices as shown in FIG. 2A. The additional input devices of theload control system 100 may comprise a wall-mounted occupancy sensor250, a temperature sensor 252, a humidity sensor, a security sensor, aproximity sensor, a wall-mounted keypad 254, a remote control keypad255, a key fob, a cell phone, a smart phone 256, a tablet 258, apersonal digital assistant (PDA), a personal computer 259, a timeclock,an audio-visual control, or safety devices, such as, fire protection,water protection, and medical emergency devices. In addition, the inputdevices may comprise one or more partition switches that transmit RFsignals in dependence upon whether a partition is opened or closed. Theinput devices may further comprise a central control transmitter toallow for central control of the fluorescent lamps 104. Specifically,the central control transmitter may be adapted to transmit a digitalmessage including one of: a timeclock command, a load shed command, ademand response command, a peak demand command, or time-of-day pricinginformation. In addition, the digital ballast controller 120 could beoperable to transmit information, such as the status and energyconsumption of the controlled loads, back to the central controltransmitter or one of the other input devices. One or more of thedifferent types of input devices may be provided in a single loadcontrol system.

Alternatively, the input devices could comprise wired transmittersoperable to transmit control signals to the controller via a wiredcontrol link, for example, a digital communication link operating inaccordance with a predefined communication protocol (such as, forexample, one of Ethernet, IP, XML, Web Services, QS, DMX, BACnet,Modbus, LonWorks, and KNX protocols), a serial digital communicationlink, an RS-485 communication link, an RS-232 communication link, adigital addressable lighting interface (DALI) communication link, aLUTRON ECOSYSTEM communication link, or a analog control link. Inaddition, the wired transmitter could be adapted to produce one of aline-voltage control signal, a phase-control signal, a 0-10V controlsignal, and a contact closure output control signal.

Alternatively, the digital ballast controller 120 may comprise differentform factors as shown in FIG. 2B. For example, the digital ballastcontroller 120 may not include the user interface, but could simplycomprise an in-wall device 260 adapted to be mounted inside anelectrical wallbox and to receive the RF signals from the wirelessoccupancy sensor 130, the wireless daylight sensor 140, and the wirelessbattery-powered remote control 150. In addition, the digital ballastcontroller 120 could alternatively be mounted to a ceiling, in anelectrical panel, to a DIN rail in an electrical closet (e.g., device262 in FIG. 2B), or to a junction box behind a wall or above a ceiling(e.g., device 264 in FIG. 2B). Further, the digital ballast controller120 could comprise a multi-zone lighting control device 266, such as aGRAFIK EYE control unit, which is adapted to be mounted in a multi-gangelectrical wallbox and has an advanced user interface for configuringand adjusting the controlled lighting loads.

The ballasts 110 could alternatively be digital switching ballasts thatare only responsive to digital messages transmitted by the digitalballast controller 120 that include commands to turn the respectivelamps on and off. The digital switching ballasts would not be responsiveto commands to adjust the intensity of the respective lamp 104 acrossthe dimming range of the ballast, i.e., between the low-end intensityL_(LE) and the high-end intensity L_(HE). However, the digital switchingballasts may be operable to adjust the high-end intensity L_(HE) inresponse to digital messages received from the digital ballastcontroller 120.

In addition, the load control system 100 could alternatively compriseload control devices for other types of electrical loads (rather thanballasts for fluorescent lamps). FIG. 2C shows examples of additionaltypes of electrical loads and load control devices that may be includedin the load control system 100. For example, the load control devices ofthe load control system 100 may also comprise a light-emitting diode(LED) driver 270 for driving an LED light source (i.e., an LED lightengine); a screw-in luminaire including a dimmer circuit and anincandescent or halogen lamp; a screw-in luminaire including a ballastand a compact fluorescent lamp; a screw-in luminaire including an LEDdriver and an LED light source; a dimming circuit for controlling theintensity of an incandescent lamp 272, a halogen lamp, an electroniclow-voltage lighting load, a magnetic low-voltage lighting load, oranother type of lighting load; an electronic switch, controllablecircuit breaker, or other switching device for turning electrical loadsor appliances on and off; a plug-in load control device 274,controllable electrical receptacle, or controllable power strip forcontrolling one or more plug-in electrical loads; a motor control unitfor controlling a motor load, such as a ceiling fan or an exhaust fan; adrive unit for controlling a motorized window treatment 276 or aprojection screen; motorized interior or exterior shutters; a thermostatfor a heating and/or cooling system; a temperature control device 278for controlling a heating, ventilation, and air conditioning (HVAC)system; an air conditioner; a compressor; an electric baseboard heatercontroller; a controllable damper; a humidity control unit; adehumidifier; a water heater; a pool pump; a TV or computer monitor; anelectric charger, such as an electric vehicle charger; and analternative energy controller (e.g., a solar, wind, or thermal energycontroller). In addition, a single digital ballast controller could becoupled to multiple types of load control devices in a single loadcontrol system.

FIG. 3A is a simplified block diagram of the digital ballast controller120. The electrical hardware of the digital ballast controller 120 isvery similar to that of a standard dimmer switch. The digital ballastcontroller 120 comprises a hot terminal H and a neutral terminal Nadapted to be coupled to the AC power source 102 and a control-hot CHterminal adapted to be coupled to the two-wire digital dimming ballasts110. The digital ballast controller 120 comprises a controllablyconductive device (CCD) 210, i.e., a controlled switch, coupled inseries electrical connection between the AC power source 102 and thedigital dimming ballasts 110 for generating the control-hot voltageV_(CH). The controllably conductive device 210 may comprise any suitabletype of bidirectional semiconductor switch, such as, for example, atriac, a field-effect transistor (FET) in a rectifier bridge, two FETsin anti-series connection, or one or more insulatated-gate bipolarjunction transistors (IGBTs). The controllably conductive device 210 isoperable to conduct a total load current L_(LOAD) of the ballasts 110and the lamps 104. The controllably conductive device 210 includes acontrol input coupled to a drive circuit 212. The digital ballastcontroller 120 further comprises a microprocessor 214 coupled to thedrive circuit 212 for rendering the controllably conductive device 210conductive or non-conductive to thus generate the control-hot voltageV_(CH) at the control-hot terminal CH. The microprocessor 214 mayalternatively comprise, for example, a microcontroller, a programmablelogic device (PLD), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or any suitable processing device,controller, or control circuit.

The microprocessor 214 is coupled to a zero-crossing detector 216, whichis coupled between the hot terminal H and the neutral terminal N fordetermining the zero-crossings of the AC power source 102. Thezero-crossings are defined as the times at which the AC supply voltageof the AC power source 102 transitions from positive to negativepolarity, or from negative to positive polarity, for example, at thebeginning (and end) of each half-cycle. The microprocessor 214 providesthe control inputs to the drive circuit 212 at predetermined timesrelative to the zero-crossings of the AC power source 102 forcontrolling the controllably conductive device 210 to be non-conductiveand conductive each half-cycle of the AC power source to thus generatethe control-hot voltage V_(CH). Specifically, the controllablyconductive device 210 is controlled to be non-conductive at thebeginning of each half-cycle and is rendered conductive at a firingtime, such that the controllably conductive device is conductive for aconductive period each half-cycle of the AC power source (i.e., thecontrol-hot voltage V_(CH) resembles a forward phase-control voltage).The microprocessor 214 is operable to adjust the firing time of thecontrollably conductive device 210 across a small range each half-cycleto communicate the digital messages (i.e., packets of digital data) tothe digital dimming ballasts 110 as will be described in greater detailbelow. In addition, if the lamps 104 of the both ballasts 110 should beoff, the microprocessor 214 may be operable to render the controllablyconductive device 210 non-conductive for the entire length of eachhalf-cycle to interrupt the load current L_(LOAD) to the ballasts, andthus, preventing the ballasts 110 from drawing any standby current fromthe AC power source 102.

As mentioned above, the microprocessor 214 renders the controllablyconductive device 210 conductive each half-cycle to generate thecontrol-hot voltage V_(CH). The control-hot voltage V_(CH) ischaracterized by a frequency (e.g., approximately twice the frequency ofthe AC mains line voltage) that is much smaller the frequency of thedigital messages transmitted by the control devices of the prior artpower-line carrier communication systems. Since the controllablyconductive device 210 is coupled between the AC power source 102 and thedigital dimming ballasts 110, the control-hot voltage V_(CH) only existson the circuit wiring 114 between the digital ballast controller 120 andthe digital dimming ballasts 110 (i.e., the digital ballast controlleroperates to “swallow” the control-hot voltage V_(CH)). Accordingly, thecontrol-hot voltage V_(CH) does not interfere with other control devicesthat may be coupled to the AC power source 102. In addition, thecontrol-hot voltage V_(CH) is not degraded by a reactive element thatmay be coupled in parallel with the AC power source 102, for example, alarge capacitance due to the other control devices coupled in parallelwith the AC power source.

Since the electrical hardware of the digital ballast controller 120 isvery similar to that of a standard dimmer switch, the microprocessor 214could be controlled to alternately operate in a dimmer mode and adigital communication mode. In the dimmer mode, the microprocessor 214could render the controllably conductive device 210 conductive at aphase angle each half-cycle that is dependent upon the desired lightingintensity L_(DES) to control one or more prior art dimmable two-wireballasts, for example, a screw-in compact fluorescent lamp having anintegral dimmable electronic ballast circuit. In the digitalcommunication mode, the microprocessor 210 could render the controllablyconductive device 210 conductive each half-cycle to generate thecontrol-hot voltage V_(CH) to transmit digital messages to the digitaldimming ballasts 110 as described herein. Accordingly, the digitalballast controller 120 could be field-configurable to operate in thedimmer mode and the digital communication mode (e.g., using an advancedprogramming mode) depending upon the type of loads to which the digitalballast controller is coupled. An example of an advanced programmingmode for a wall-mounted load control device is described in greaterdetail in U.S. Pat. No. 7,190,125, issued Mar. 13, 2007, entitledPROGRAMMABLE WALLBOX DIMMER, the entire disclosure of which is herebyincorporated by reference.

The microprocessor 214 receives inputs from the toggle actuator 124 andthe intensity adjustment actuator 126 and controls the status indicators128. The microprocessor 214 is also coupled to a memory 218 for storageof the preset intensities of fluorescent lamps 104 and the serial numberof wireless transmitters (i.e., the occupancy sensor 130, the daylightsensor 140, and the remote control 150) to which the digital ballastcontroller 120 is associated. The memory 218 may be implemented as anexternal integrated circuit (IC) or as an internal circuit of themicroprocessor 214. A power supply 220 is coupled between the hotterminal H and the neutral terminal H and generates a direct-current(DC) supply voltage V_(CC) for powering the microprocessor 214, thememory 218, and other low-voltage circuitry of the digital ballastcontroller 120.

The digital ballast controller 120 further comprises an RF receiver 222and an antenna 224 for receiving the RF signals 106 from the wirelesscontrol devices (i.e., the occupancy sensor 130, the daylight sensor140, and the remote control 150). The microprocessor 214 is operable tocontrol the controllably conductive device 210 in response to themessages received via the RF signals 106. Examples of antennas forwall-mounted control devices, such as the digital ballast controller120, are described in greater detail in U.S. Pat. No. 5,982,103, issuedNov. 9, 1999, and U.S. Pat. No. 7,362,285, filed Apr. 22, 2008, bothentitled COMPACT RADIO FREQUENCY TRANSMITTING AND RECEIVING ANTENNA ANDCONTROL DEVICE EMPLOYING SAME, the entire disclosures of which arehereby incorporated by reference. Alternatively, the RF receiver 222could comprise an RF transceiver for both receiving and transmitting theRF signals 106.

FIG. 3B is a simplified block diagram of one of the digital dimmingballasts 110. The ballast 110 comprises a control-hot terminal CH and aneutral terminal N that are adapted to be coupled to analternating-current (AC) power source (not shown) for receiving thecontrol-hot voltage V_(CH) from the digital ballast controller 120. Eachdigital dimming ballast 110 comprises an RFI (radio frequencyinterference) filter circuit 310 for minimizing the noise provided onthe AC mains, and a rectifier circuit 320 for generating a rectifiedvoltage V_(RECT) from the control-hot voltage V_(CH). The digitaldimming ballast 110 may further comprises a boost converter 330 forgenerating a direct-current (DC) bus voltage V_(BUS) across a buscapacitor C_(BUS). The DC bus voltage V_(BUS) typically has a magnitude(e.g., approximately 465 V) that is greater than the peak magnitudeV_(PK) of the control-hot voltage V_(CH) (e.g., approximately 170 V).The boost converter 330 also operates as a power-factor correction (PFC)circuit for improving the power factor of the ballast 110. The digitaldimming ballast 110 also includes a load regulation circuit 340comprising an inverter circuit 342 for converting the DC bus voltageV_(BUS) to a high-frequency AC voltage V_(INV) and a resonant tankcircuit 344 for coupling the high-frequency AC voltage V_(INV) generatedby the inverter circuit to filaments of the lamp 104.

The digital dimming ballast 110 further comprises a microprocessor 360for controlling the intensity of the fluorescent lamp 104 to the desiredlighting intensity L_(DES) between the low-end intensity L_(LE) and thehigh-end intensity L_(HE). The microprocessor 360 may alternativelycomprise, for example, a microcontroller, a programmable logic device(PLD), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or any suitable processing device,controller, or control circuit. The microprocessor 360 is coupled to amemory 362 for storage of the control information of the digital dimmingballast 110. The digital dimming ballast 110 also comprises a powersupply 364, which receives the bus voltage V_(BUS) and generates a DCsupply voltage V_(CC) (e.g., approximately five volts) for powering themicroprocessor 360, the memory 362, and the other low-voltage circuitryof the ballast.

The microprocessor 360 provides a drive control signal V_(DRIVE) to theinverter circuit 342 for controlling the magnitude of a lamp voltageV_(L) generated across the fluorescent lamp 104 and a lamp current I_(L)conducted through the lamp. Accordingly, the microprocessor 360 isoperable to turn the fluorescent lamp 104 on and off and adjust (i.e.,dim) the intensity of the lamp. The microprocessor 360 receives a lampcurrent feedback signal V_(FB-IL), which is generated by a lamp currentmeasurement circuit 370 and is representative of the magnitude of thelamp current I_(L). The microprocessor 360 also receives a lamp voltagefeedback signal V_(FB-VL), which is generated by a lamp voltagemeasurement circuit 372 and is representative of the magnitude of thelamp voltage V_(L).

The ballast 110 comprises an edge detect circuit 380 for receiving therectified voltage V_(RECT) and generating an edge-detect control signalV_(ED) that is received by the microprocessor 360. For example, the edgedetect circuit 380 may drive the edge-detect control signal V_(ED) high(i.e., to approximately the DC supply voltage V_(CC)) when the magnitudeof the control-hot voltage V_(CH) rises above a rising thresholdV_(TH-R) (e.g., approximately 20 volts), and drives the edge-detectcontrol signal V_(ED) low when the magnitude of the control-hot voltageV_(CH) drops below a falling threshold V_(TH-F) (e.g., approximately 10volts). The microprocessor 360 is operable to determine the firing angleof the control-hot voltage V_(CH) each half-cycle of the AC power sourcein order to receive the digital messages transmitted by the digitalballast controller 120 as will be described in greater detail below.

The digital dimming ballast 110 could be controlled to alternatelyoperate in a dimmer mode and a digital communication mode. In the dimmermode, the ballast 110 may be operable to receive a standardphase-control signal from a prior-art dimmer switch and to determine thedesired lighting intensity L_(DES) for the lamp 104 in response to thelength of the conduction period of the phase-control voltage. In thedigital communication mode, the ballast 100 may be operable to receivethe control-hot voltage V_(CH) from the digital ballast controller 120and to determine the desired lighting intensity L_(DES) in response tothe digital messages decoded from the control-hot voltage V_(CH).

The microprocessor 360 is operable to determine a control channel (oraddress) of the digital dimming ballast 110 in response to a channelsetting circuit, e.g., two or more DIP (dual in-line package) switches382. For example, four channels may be selected by adjusting thepositions of two DIP switches. Alternatively, the digital dimmingballast 110 could comprise rotary encoder or a plurality of jumpers forselecting the control channel. In addition, the control channel couldalternatively be selected in response to digital messages received fromthe digital ballast controller 120 (e.g., automatically assigned using a“soft-addressing” procedure or manually selected by a user via agraphical user interface running on a computer). According to the firstembodiment of the present invention, each digital dimming ballast 110may only be assigned to one control channel at a time. However, thedigital dimming ballasts 100 could alternatively be assigned to multiplecontrol channels according to alternate embodiments of the presentinvention. In addition, the digital dimming ballast 110 couldalternatively comprise a different DIP switch for each of the pluralityof types of wireless transmitters to which the ballast may be responsive(e.g., the occupancy sensor 130, the daylight sensor 140, and the remotecontrol 150). The DIP switch for a specific type of wireless transmittercould be selected (by adjusting the position of the DIP switch) toenable control of the digital dimming ballast 110 in response to thattype of wireless transmitter.

The microprocessor 260 determines how the digital dimming ballastoperates in response to the various inputs (i.e., the actuations of thetoggle actuator 124 and the intensity adjustment actuator 126 or the RFsignals 106 received from the occupancy sensor 130, the daylight sensor140, and the remote control 150) in dependence upon the selected controlchannel an well as control information stored in the memory 362. Thecontrol channel may determine which of the wireless transmitters (i.e.,the occupancy sensor 130, the daylight sensor 140, and the remotecontrol 150) to which the digital dimming ballast 110 is responsive. Inaddition, the microprocessor 360 may determine if the digital dimmingballast 110 should respond to actuations of the user interface of thedigital ballast controller 120 (i.e., the toggle actuator 124 and theintensity adjustment actuator 126) in response to the control channel.Since the digital dimming ballasts 110 determine the control channel inresponse to the positions of the DIP switches 382 and the digitalballast controller 120 is associated with the wireless transmitters viaa manual procedure (i.e., pressing an actuator on the wirelesstransmitter and pressing an actuator on the digital ballast controller),the load control system 100 requires no advanced computing device (e.g.,a personal computer or laptop) to be programmed and configured afterinstallation.

For example, the ballast 110 may respond to the various inputs independence upon the control channel as shown in the following table(i.e., which may be stored in the memory 362).

Channel Respond to . . . 1 User interface of digital ballast controllerOccupancy Sensors Remote Control #1 2 User interface of digital ballastcontroller Occupancy Sensors Daylight Sensors Remote Control #1 3 Userinterface of digital ballast controller Remote control #2 4 Userinterface of digital ballast controller Occupancy Sensors Remote Control#2When the digital ballast controller 120 receives one of the variousinputs (i.e., the actuations of the toggle actuator 124 and theintensity adjustment actuator 126 or the RF signals 106 received fromthe occupancy sensor 130, the daylight sensor 140, and the remotecontrol 150), the digital ballast controller 120 transmits digitalmessages including information regarding the channels associated withthe source of the control information to the digital dimming ballasts110. For example, if the digital ballast controller 120 receives anoccupied command from the occupancy sensor 130, the digital ballastcontroller will include information regarding channels 1, 2, and 4 inthe digital message that is subsequently transmitted to the digitaldimming ballasts 110.

The load control system 100 allows for easy retrofitting to upgradefrom, for example, an older non-dim ballast system. Once installed, thedigital dimming ballasts 110 are able to receive power over the existingbuilding wiring, and the digital ballast controller 120 is able totransmit digital messages to the ballasts over the existing buildingwiring. In other words, the load control system 100 requires noadditional wiring and provides both power and communication over the twowires between the AC power source 102 and the digital dimming ballasts110. Since the load control system 100 requires no additional wiring andno advanced computing device to be programmed, the load control systemprovides economic savings in regards to installation and servicing, andprovides a cognitive benefit to those installing and servicing the loadcontrol system. In addition, the digital dimming ballasts 110 may beeasily replaced in the event of a ballast failure since the controlchannel is simply determined from the positions of the DIP switches 382(which may be effortlessly adjusted to match the ballast that is beingreplaced). Further, the digital dimming ballasts 110 allow users of thesystem to control their visual environment, thereby improving end usercomfort and productivity.

FIG. 4A is a floor plan diagram of a first installation of the loadcontrol system 100 in a classroom 160. The classroom 160 has apresentation board 162 and a desk 164 at the front end and three windows166 at the back end. The classroom 160 includes nine lighting fixtures112A-112J, which each include a respective two-wire digital dimmingballast 110A-110J driving two fluorescent lamps 104. A digital ballastcontroller 120 is mounted in an electrical wallbox adjacent thepresentation board 162 and is electrically coupled to the ballasts110A-110J via the circuit wiring 114 for coupling the control-hotvoltage V_(CH) and the neutral side of the AC power source 102 to eachballast. The occupancy sensor 130 and the daylight sensor 140 aremounted to the ceiling of the classroom 160 near the center of the room,and two remote controls 150A, 150B are located on the desk 164.

For example, the digital dimming ballasts 110 could replace standardnon-dim ballasts, and the digital ballast controllers 120 could replacestandard mechanical switches. The digital ballast controller 120 is ableto control ballasts 110A-110J in groups, for example, depending upon thedistance of the fixtures 112A-112J from the front end or the back end ofthe classroom 160. According to the example installation of FIG. 4A, allof the ballasts 110A-110J in the classroom 160 are responsive toactuations of the user interfaces of the digital ballast controller 120.Only the ballasts 110C, 110F, 110J closest to the windows 166 adjust theintensities of the controlled fluorescent lamps 104 in response to thedaylight sensor 140. The ballasts 110A, 110D, 110G closest to thepresentation board 162 are controlled by the second remote control 150B,while the remaining ballasts 110B, 110C, 110E, 110F, 110H, 110J arecontrolled by the occupancy sensor 130 and the first remote control150A.

To provide this functionality, the ballasts 110A, 110D, 110G in a firstgroup 170 closest to the presentation board 162 are assigned controlchannel 3, the ballasts 110B, 110E, 110H in a second group 172 in thecenter of the room are assigned control channel 1, and the ballasts110C, 110F, 110J in a third group 174 closest to the windows 166 areassigned control channel 2 (as detailed in the table shown above).Therefore, the ballasts 110A, 110D, 110G in the first group 170 respondto the user interfaces of the respective digital ballast controller 120and the second remote control 150B. The ballasts 110B, 110E, 110H in thesecond group 172 respond to the user interfaces of the respectivedigital ballast controllers 120A-120C, the occupancy sensor 130, and thefirst remote control 150A. The ballasts 110C, 110F, 110J in the thirdgroup 174 respond to the user interfaces of the respective digitalballast controller 120, the occupancy sensor 130, the daylight sensor140, and the first remote control 150A.

If all of the lamps 104 controlled by the digital dimming ballasts110A-110J on the circuit wiring 114 should be off, the digital ballastcontroller 120 can render the controllably conductive device 210non-conductive to disconnect the ballasts from the AC power source 102,and thus prevent the ballasts from drawing any standby current from theAC power source. In addition, one or more of the ballasts 110A-110Jcould comprise prior art non-dim ballasts that would not be responsiveto any digital messages transmitted by the digital ballast controller120 to the digital dimming ballasts in the classroom 160. The non-dimballasts would each simply remain at the high-end intensity L_(HE) whilethe digital dimming ballasts are controlled through the dimming range bythe digital ballast controller 120. The digital ballast controller 120could turn off the non-dim ballasts (as well as the digital dimmingballasts) by rendering the controllably conductive device 210non-conductive. As previously mentioned, the ballasts couldalternatively comprise digital switching ballasts that are responsive todigital messages transmitted by the digital ballast controller 120, butonly to commands to turn the respective lamps on and off.

FIG. 4B is a floor plan diagram of a second example installation of theload control system 100 in a classroom 160′. The classroom 160′ of FIG.4B includes three different circuit wirings 114A, 114B, 114C providingpower to the ballasts 110A-110J, and thus three digital ballastcontrollers 120A, 120B, 120C, which are mounted in electrical wallboxesadjacent the presentation board 162. The first three ballasts 110A,110B, 110C are electrically coupled to the first digital ballastcontroller 120A via the first circuit wiring 114A. In addition, ballasts110D, 110E, 110F are electrically coupled to the second digital ballastcontroller 120B via the second circuit wiring 114B, and ballasts 110G,110H, 110J are electrically coupled to the third digital ballastcontroller 120C via the third circuit wiring 114C.

The digital ballast controllers 120A, 120B, 120C of FIG. 4B are able tocontrol the ballasts 110A-110J in the three groups 170, 172, 174, i.e.,depending upon the distance of the fixtures 112A-112J from the front endor the back end of the classroom 160′. Accordingly, the digital ballastcontrollers 120A, 120B, 120C are able to control the ballasts 110A-110Jin response to the occupancy sensor 130, the daylight sensor 140, andthe remote controls 150A, 150B independent of the specific circuitwirings 114A, 114B, 114C that extend from the front end to the back endof the classroom 160′ (i.e., perpendicular to the groups 170, 172, 174).All of the ballasts 110A-110J in the classroom 160′ are responsive toactuations of the user interfaces of the respective digital ballastcontrollers 120A-120C. Only the ballasts 110C, 110F, 110J closest to thewindows 116 adjust the intensities of the controlled fluorescent lamps104 in response to the daylight sensor 140. The ballasts 110A, 110D,110G closest to the presentation board 162 are controlled by the secondremote control 150B, while the remaining ballasts 110B, 110C, 110E,110F, 110H, 110J are controlled by the occupancy sensor 130 and thefirst remote control 150A.

Since each of the digital ballast controllers 120A, 120B, 120C operatesto swallow the digital messages transmitted to the ballasts 110A-110J onthe respective circuit wirings 114A, 114B, 114C, these digital messagesare not received the other digital ballast controllers and thus do notinterfere with the other digital ballast controllers. However, each ofthe digital ballast controllers 120A, 120B, 120C may be operable totransmit digital messages to the other digital ballast controllers viaRF signals. Specifically, the digital ballast controller 120A, 120B,120C may be operable to transmit digital messages to the other digitalballast controllers in response to actuations of the user interfaces,such that all of the ballasts 110A-110J in the classroom 160 may beresponsive to actuations of the user interfaces of any of the digitalballast controllers.

FIG. 5 is a simplified perspective view of a retrofit kit 180 having oneof the two-wire digital dimming ballasts 110 mounted to a pan 182, whichis designed to be easily installed in a lighting fixture. The retrofitkit 180 further comprises two pairs of dimmable lamp sockets 184 thatare mounted to the pan 182 and are pre-wired to the digital dimmingballast 110 via electrical wires 185. Each pair of sockets 184 isoperable to be coupled to, for example, a U-bend fluorescent lamp asshown in FIG. 5. Alternatively, the sockets 184 could be mounted atopposite ends of the pan 182 to thus be adapted to be coupled to astraight fluorescent lamp. In addition, the retrofit kit 180 couldcomprise more or less sockets 184 to allow the ballast 110 to be coupledto a different number of lamps. The retrofit kit 180 further comprises acontrol-hot electrical wire 186 and a neutral electrical wire 188 forcoupling the ballast 110 to the circuit wiring of the building.Accordingly, to provide for easy retrofit installation, the retrofit kit180 may be assembled prior to shipment to a customer. The old pan of theballast being replaced can simply be removed from a lighting fixture andthe new retrofit kit 180 can be installed into the lighting fixture itsplace with the only required electrical connections being thecontrol-hot electrical wire 186 and the neutral electrical wire 188 tothe circuit wiring of the building.

FIG. 6 is a simple timing diagram of the control-hot voltage V_(CH)according to the first embodiment of the present invention showing adata pattern of one of the transmitted digital messages. As previouslymentioned, each digital ballast controller 120 is operable to adjust thefiring time of the respective controllably conductive device 210 acrossa small time window T_(WIN) (e.g., approximately 300 microseconds) eachline cycle to communicate the digital messages to the respective digitaldimming ballasts 110. Digital information (i.e., bits of the transmitteddigital messages) is encoded in the firing times of timing edges (i.e.,transitions) of the control-hot voltage V_(CH). Specifically, the bitsof the transmitted digital messages are encoded in the firing time of adata edge (i.e., a data edge time) of the controllably conductive device210 as measured with respect to a firing time of a reference edge (i.e.,a reference edge time) in a previous half-cycle. In other words, thebits of the transmitted digital messages are encoded as a function ofthe firing times of the reference and data edges. Each data patternincludes a half-cycle having a reference edge and a number N_(DP) ofsubsequent half-cycles having data edges. Each reference edge is spacedat a reference edge time period T_(REF) (e.g., approximately 1.3milliseconds) from the zero-crossing of the present half-cycle.According to the first embodiment of the present invention, there is onedata edge for each reference edge (i.e., the number N_(DP) ofhalf-cycles having data edges equal one).

The value of the digital data transmitted by the digital ballastcontroller 120 is dependent upon an offset time period T_(OS) (i.e., adifference) between the data edge and the previous reference edge (i.e.,in the previous half-cycle). The digital ballast controller 120 maycontrol the data edges to be at one of four times across the time windowT_(WIN), thus resulting in one of four offset time periods T_(OS1),T_(OS2), T_(OS3), T_(OS4), from the previous reference edge, such thattwo bits may be transmitted each line cycle. To transmit bits “00”, thedigital ballast controller 120 is operable to render the controllablyconductive device 210 conductive at the first possible data edge time,such that the first offset time period T_(OS1) (e.g., approximately 8.33milliseconds) exists between the reference edge and the data edge. Forexample, each of the possible data edge times may be approximately 100microseconds apart, and the rise time of the control-hot voltage V_(CH)at the data edges is less than approximately 10 microseconds.

Accordingly, the digital ballast controller 120 is operable to controlthe offset time period T_(OS) between the reference edge and the dataedge to the second offset time period T_(OS2) (e.g., approximately 8.43milliseconds) to transmit bits “01”, to the third offset time periodT_(OS3) (e.g., approximately 8.53 milliseconds) to transmit bits “10”,and the fourth offset time period T_(OS4) (e.g., approximately 8.63milliseconds) to transmit bits “11” as shown in FIG. 6. Themicroprocessor 360 of each digital ballast 110 determines if the offsettime period T_(OS) of each data pattern is approximately equal to one ofthe four offset time periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) within adefault tolerance ΔT_(OS), which may be equal to, for example,approximately fifty microseconds. Alternatively, the number of dataedges possible in the time window T_(WIN) could be greater than four,for example, eight in order to transmit three bits of data each linecycle.

When the digital ballast controller 120 is not transmitting a digitalmessage to the digital dimming ballasts 110, the digital ballastcontroller continues to render the controllably conductive device 210conductive as if the digital ballast controller was continuouslytransmitting bits “00.” Specifically, the digital ballast controller 120renders the controllably conductive device 210 conductive after thereference time T_(REF) from the zero-crossing in a first half-cycle ofeach line cycle and renders the controllably conductive deviceconductive after the first offset time period T_(OS1) in the otherhalf-cycle of the line cycle as measured form the reference time t_(REF)in the previous half-cycle, such that the control-hot voltage V_(CH)generated by the digital ballast controller has at least one timing edgein each half-cycle of the AC power source 102. Because the control-hotvoltage V_(CH) has at least one timing edge in each half-cycle, thedigital dimming ballasts 110 do not have zero-crossing detectors havinglow voltage thresholds that may be susceptible to noise on the AC mainsline voltage, thus causing communication reception errors. Rather, thedigital dimming ballasts 110 include the edge detect circuit 380 havingthe rising threshold V_(TH-R) (i.e., approximately 20 volts), which islarge enough, such that the digital dimming ballasts 110 has an enhancenoise immunity to typical noise on the AC mains line voltage.

Alternatively, the digital ballast controller 120 could render thecontrollably conductive device 210 fully conductive (i.e., forapproximately the length of each half-cycle) when the digital ballastcontroller is not transmitting a digital message (i.e., the control-hotvoltage V_(CH) is a full-conduction waveform), Accordingly, thecontrol-hot voltage V_(CH) does not have at least one timing edge ineach half-cycle when the digital ballast controller is not transmittinga digital message to the digital dimming ballasts 110.

According to another alternate embodiment, the digital dimming ballasts110 may be operable to be controlled into an emergency mode in which theballasts each control the intensity of the respective lamp 104 to thehigh-end intensity L_(HE). For example, a normally-open bypass switchcould be coupled in parallel with the digital ballast controller 120 andcould be rendered conductive during an emergency condition, such that afull-conductive waveform is provided to the control-hot terminals CH ofthe digital dimming ballasts 110. The digital dimming ballasts 110 couldeach be operable to control the intensity of the respective lamp 104 tothe high-end intensities L_(HE) in response to receiving thefull-conduction waveform at the control-hot terminal CH.

FIG. 7 is a simple diagram of the message structure for the digitalmessages transmitted by the digital ballast controller 120 to thedigital dimming ballasts 110. Each digital message comprises a totalnumber N_(DM) of bits (e.g., 20 bits). The first four bits comprises astart pattern, which includes a unique start symbol as will be describedin greater detail below with reference to FIG. 8. A channel mask of eachdigital message includes four bits, each of which may be set to indicatethe channels of the ballasts 110 that should respond to the digitalmessage. For example, if the ballasts 110 that have control channel 1should respond to the digital message, the first bit of the channel maskwill be a logic one value. The channel mask is followed by two bits thatdetermine a command type of the digital message and five bits thatinclude an intensity level for the fluorescent lamps 104 or data for theballasts 110. Finally, each digital message concludes with five bitsthat are used to determine if an error occurred during transmission andreception of the digital message (e.g., a checksum). Accordingly, eachdigital messages transmitted by the ballast controller 120 istransmitted across a predetermined (i.e., fixed) number of consecutiveline cycles, e.g., ten line cycles.

FIG. 8 is a simple timing diagram of the control-hot voltage V_(CH)showing the start pattern according to the first embodiment of thepresent invention. To transmit the start pattern, the digital ballastcontroller 120 transmits bits “00” during a first line cycle and thentransmits the unique start symbol during a second subsequent line cycleby rendering the controllably conductive device 210 conductive after astart symbol time period T_(START) after the reference edge in theprevious half-cycle. The start symbol time period T_(START) is uniquefrom the offset time periods T_(OS1)−T_(OS4) used to transmit data tothe digital dimming ballasts 110 and may be longer than the offsettimes, for example, approximately 8.73 milliseconds.

The ballasts 110 continuously monitor the control-hot voltage V_(CH) todetermine if the digital ballast controller has transmitted a startpattern including the unique start symbol. Specifically, themicroprocessor 360 of each digital dimming ballast 110 measures timeperiods T_(RE) between the rising edges in each consecutive half-cycleand stores these times in the memory 362. The microprocessor 360 looksfor three consecutive measured time periods T₁, T₂, T₃ stored in thememory 362 that have values corresponding to the start pattern as shownin FIG. 8, i.e.,T ₁ =T _(OS1),T ₂ =T _(LC) −T _(OS1), andT ₃ =T _(SP),where T_(LC) is the line-cycle time period, which represents the lengthof each line cycle of the AC power source 102. The line-cycle timeT_(LC) period may be a fixed value stored in the memory 362 (e.g.,approximately 16.66 milliseconds) or may be measured by themicroprocessor 360 (i.e., the time period between every otherzero-crossing of the AC power source 102). Because the start symbol timeperiod T_(START) is unique from the offset time periods T_(OS1)-T_(OS4)used to transmit data to the digital dimming ballasts 110, the digitalballast controller 120 is able to interrupt a first digital message thatis being transmitted in order to transmit a second digital message tothe ballasts 110 by transmitting the start symbol before the end of thefirst digital message.

Since the second time period T₂ of the three consecutive measured timeperiods is a function of the line-cycle time period T_(LC), which mayvary depending upon characteristics the load control system 100 that arenot controlled by the digital ballast controller 120, the microprocessor360 determines if the second time period T₂ is equal to the line-cycletime period T_(LC) minus the first offset time period T_(OS1) within awidened tolerance ΔT_(OS-W), which is greater than the default toleranceΔT_(OS), for example, approximately 100 microseconds. Because thedigital ballast controller 120 requires four half-cycles to transmit thestart pattern, the start pattern takes up 4 bits of each digital messageas shown in FIG. 7. After transmitting the start pattern, the digitalballast controller 120 is operable to immediately begin transmittingdata in the next line cycle by generating a reference edge in the nexthalf-cycle and a data edge in the subsequent half-cycle as shown in FIG.8.

FIG. 9 is a simplified flowchart of a button procedure 400 executed bythe microprocessor 214 of the digital ballast controller 120 in responseto an actuation of one of the actuators of the user interface at step410 in, for example, the example installation of FIGS. 4A and 4B. Themicroprocessor 214 uses a transmit (TX) buffer to store digital messagesto transmit to the digital dimming ballasts 110. If the toggle actuator124 was actuated at step 412, the microprocessor 214 loads a digitalmessage having a toggle command into the TX buffer at step 414, and setsthe channel mask of the digital message equal to “1111” at step 416before the button procedure 400 exits. Accordingly, all of the digitaldimming ballasts 110 will toggle the controlled lamps 104 (from off toon or from on to off) in response to receiving the transmitted digitalmessage.

If the toggle actuator 124 was not actuated at step 412, but theintensity adjustment actuator 126 was actuated at step 418, themicroprocessor 214 determines if the upper potion 126A or the lowerportion 126B of the intensity adjustment actuator was just pressed orreleased. If the upper portion 126A of the intensity adjustment actuator126 was pressed at step 420, the microprocessor 214 loads a digitalmessage having a start raise command into the TX buffer at step 422, andsets the channel mask of the digital message equal to “1111” at step 416before the button procedure 400 exits. If the upper portion 126A of theintensity adjustment actuator 126 was released at step 424, themicroprocessor 214 loads a digital message having a stop raise commandinto the TX buffer at step 426. If the lower portion 126B of theintensity adjustment actuator 126 was pressed at step 428, themicroprocessor 214 loads a digital message having a start lower commandinto the TX buffer at step 430. If the lower portion 126B of theintensity adjustment actuator 126 was released at step 432, themicroprocessor 214 loads a digital message having a stop lower commandinto the TX buffer at step 434.

FIGS. 10A and 10B are simplified flowcharts of an RF message procedure500 executed by the microprocessor 214 of the digital ballast controller120 when digital message is received from one of the occupancy sensor130, the daylight sensor 140, and the remote control 150 via the RFsignals 106 at step 510. If the received digital message is from theoccupancy sensor 130 at step 512 and includes an occupied command atstep 514, the microprocessor 214 loads a digital message having an oncommand into the TX buffer at step 516 and sets the channel mask of thedigital message equal to “1101” at step 518, before the RF messageprocedure 500 exits. If the received digital message includes a vacantcommand at step 520, the microprocessor 214 loads a digital messagehaving an off command into the TX buffer at step 524 sets the channelmask equal to “1101” at step 518. If the received digital message is notfrom the occupancy sensor 130 at step 512, but is from the daylightsensor 140 at step 526, the microprocessor 214 loads a digital messageincluding the total light intensity L_(T-SNSR) measured by the daylightsensor 140 into the TX buffer at step 528, and sets the channel maskequal to “0100” at step 530, before the RF message procedure 500 exits.

Referring to FIG. 10B, if the received digital message is from one ofthe remote controls 150A, 150B at step 532 and the on button 152 wasactuated at step 534, the microprocessor 214 loads a digital messagehaving an on command into the TX buffer at step 536. If the receiveddigital message is from the first remote control 150A at step 538, themicroprocessor 214 sets the channel mask of the digital message in theTX buffer equal to “1100” at step 540 and the RF message procedure 500exits. However, if the received digital message is from the secondremote control 150B at step 538, the microprocessor 214 sets the channelmask of the digital message equal to “0011” at step 542, before the RFmessage procedure 500 exits. If the off button 154 was actuated at step544, the microprocessor 214 loads a digital message having an offcommand into the TX buffer at step 546, before setting the channel maskto either “1100” or “0011” at steps 540, 542, respectively.

If the raise button 155 was just pressed at step 548, the microprocessor214 loads a digital message having a start raise command into the TXbuffer at step 550. If the raise button 155 was released at step 552,the microprocessor 214 loads a digital message having a stop raisecommand into the TX buffer at step 554. If the lower button 156 was justpressed at step 556, the microprocessor 214 loads a digital messagehaving a start lower command into the TX buffer at step 558. If thelower button 156 was released at step 560, the microprocessor 214 loadsa digital message having a stop lower command into the TX buffer at step562. Finally, if the preset button 158 was pressed at step 564, themicroprocessor 214 loads a digital message having a preset command intothe TX buffer at step 566, before the microprocessor sets the channelmask at steps 540, 542, and the RF message procedure 500 exits.

FIG. 11 is a simplified flowchart of a zero-crossing procedure 600executed by the microprocessor 214 of each digital ballast controller120 periodically, e.g., once every half-cycle at the zero-crossing ofthe present half-cycle as determined from the zero-crossing detector 216at step 610. The microprocessor 214 uses a timer that is alwaysincreasing in value with respect to time to determine when to render thecontrollably conductive device 210 conductive to generate the referenceedges and the data edges. The microprocessor 214 also uses a variable mto keep track of whether the next rising edge of the control-hot voltageV_(CH) is a reference edge (e.g., if the variable m equals zero) or adata edge (e.g., if the variable m equals one). If the variable m isequal to zero at step 612 at the present zero-crossing (i.e., thedigital ballast controller 120 should generate a reference edge duringthe present half-cycle), the microprocessor 214 sets a timer interruptfor an interrupt time equal to a present value t_(TIMER) of the timerplus the reference time T_(REF) at step 614. When the value t_(TIMER) ofthe timer reaches the set intertupt time for the timer interrupt, themicroprocessor 214 will render the controllably conductive device 210conductive during a timer interrupt procedure 700, which will bedescribed in greater detail below with reference to FIG. 12. If thevariable m is equal to one at step 612 (i.e., the digital ballastcontroller 120 should generate a data edge during the presenthalf-cycle), the zero-crossing procedure 600 simply exits.

FIG. 12 is a simplified flowchart of the timer interrupt procedure 700that is executed by the microprocessor 214 of each digital ballastcontroller 120 to generate the reference and data edges of thetransmitted digital messages according to the second embodiment of thepresent invention. The microprocessor 214 executes the timer interruptprocedure 700 when the value of the timer equals the set interrupt time,for example, as set during the zero-crossing procedure 600. Themicroprocessor 214 first renders the controllably conductive device 210conductive at step 712. If the variable m is equal to zero at step 714(i.e., a reference edge was generated at step 712), the microprocessor214 sets a base time t₀ equal to the present value of the timer (i.e.,the time at which the reference edge was generated) at step 716. Themicroprocessor 214 then prepares to generate a data edge in the nexthalf-cycle by setting the variable m to one at step 718 and executing adata edge procedure 800, which will be described in greater detail belowwith reference to FIG. 13. The microprocessor 214 uses the base time t₀of the reference edge during the data edge procedure 800 to accuratelyset up a timer interrupt for generating the data edge in the nexthalf-cycle. If the variable m is equal to one at step 714 (i.e., a dataedge was generated at step 712), the microprocessor 214 sets thevariable m to zero at step 720 and the timer interrupt procedure 700exits, such that the microprocessor will generate a reference edgeduring the next half-cycle.

FIG. 13 is a simplified flowchart of the data edge procedure 800, whichis executed during the timer interrupt procedure 700 in order to set upa timer interrupt to generate the data edges of the control-hot voltageV_(CH). If the microprocessor 214 is not presently transmitting adigital message to the digital dimming ballasts 110 at step 810, themicroprocessor sets the interrupt time of the next timer interrupt equalto the base time t₀ (as determined at step 716 of the timer interruptprocedure 700) plus the first offset time period T_(OS1) at step 812,before the data edge procedure 800 exits. The microprocessor 214continues to render the controllably conductive device 210 conductive asif the microprocessor was continuously transmitting bits “00” while themicroprocessor is not transmitting digital messages to the digitaldimming ballasts 110.

If the microprocessor 214 is transmitting a digital message to thedigital dimming ballasts 110 at step 810, the microprocessor 214determines if a start symbol is presently being transmitted at step 814.If the microprocessor 214 is presently transmitting a start symbol atstep 814 and is presently transmitting the first two bits of the startsymbol at step 815, the microprocessor 214 sets the interrupt time ofthe next timer interrupt equal to the base time t₀ plus the first offsettime period T_(OS1) at step 816 and the data edge procedure 800 exits.If the microprocessor 214 is presently transmitting the last two bits ofthe start symbol at step 815, the microprocessor 214 sets a timerinterrupt for the interrupt time of the next timer interrupt equal tothe base time t₀ plus the start symbol time T_(SP) at step 818 and setsa variable n to one at step 820, before the data edge procedure 800exits. The microprocessor 214 uses the variable n to keep track of whichbits of the present digital message in the TX buffer are presently beingtransmitted, where a value of one for the variable n represents thefirst bit and a value equal to the total number N_(DM) of bits of thedigital message represents the last bit of the digital message.

If the microprocessor 214 is transmitting a digital message to thedigital dimming ballasts 110 at step 810, but is not transmitting astart symbol at step 814, the microprocessor transmits the data patternsof the digital message. If the next two bits TX[n+1,n] of the digitalmessage in the TX buffer are equal to “00” at step 822, themicroprocessor 214 sets the interrupt time of the next timer interruptequal to the base time t₀ plus the first offset time period T_(OS1) atstep 824. If the next two bits TX[n+1,n] of the digital message in theTX buffer are equal to “01” at step 826, equal to “10” at step 830, orequal to “11” at step 834, the microprocessor 214 sets the interrupttime of the next timer interrupt equal to the base time t₀ plus thesecond offset time period T_(OS2) at step 828, the base time t₀ plus thethird offset time period T_(OS3) at step 832, or the base time t₀ plusthe fourth offset time period T_(OS4) at step 836, respectively.

If the variable n is not equal to the total number N_(DM) of bits of thedigital message minus one at step 838, the microprocessor 214 increasesthe variable n by two at step 840 (since two bits are transmitted eachline cycle). If there is the microprocessor 214 does not have a higherpriority message to transmit and should not interrupt the digitalmessage that is presently being transmitted at step 842, the data edgeprocedure 800 simply exits. However, if the microprocessor 214 shouldinterrupt the digital message presently being transmitted at step 842,the microprocessor 214 clears the last digital message out of the TXbuffer at step 844, before the data edge procedure 800 exits. If thevariable n is equal to the total number N_(DM) of bits of the digitalmessage minus one at step 838 (i.e., the present digital message iscomplete), the microprocessor 214 also clears the last digital messageout of the TX buffer at step 844, and the data edge procedure 800 exits.

FIG. 14 is a simplified flowchart of a receiving procedure 900 executedby the microprocessor 360 of each digital dimming ballast 110periodically (e.g., once every half-cycle) to receive the digitalmessages transmitted by the connected digital ballast controller 120.Specifically, the transmission procedure 900 is executed when a risingedge of the control-hot voltage V_(HC) (i.e., a reference edge or a dataedge) is detected at step 910 (i.e., in response to the edge-detectcontrol signal V_(ED) generated by the edge detect circuit 380). Themicroprocessor 360 uses a receive (RX) buffer to store the bits of thedigital messages as they are being received, so that the digital messagecan be stored until the microprocessor processes the messages to thuscontrol the fluorescent lamps 104.

As previously mentioned, the microprocessor 360 continually monitors thecontrol-hot voltage V_(CH) to determine if the digital ballastcontroller 120 has transmitted a start pattern including the uniquestart symbol by measuring the time period between the times of therising edges in each consecutive half-cycle and storing these timeperiods in the memory 362. Specifically, the microprocessor 360 sets arising edge time t_(E) equal to the present value t_(TIMER) of the timerat step 912, and then determines the last three time periods T₁, T₂, T₃between the rising edges of the control-hot voltage V_(CH) at step 914by setting the first time period T₁ equal to the previous second timeperiod T₂, setting the second time period T₂ equal to the previous thirdtime period T₃, and setting the third time period T₃ equal to the risingedge time t_(E) minus a previous rising edge time t_(E-PREV).

Next, the microprocessor 360 determines if the last three time periodsT₁, T₂, T₃ between the rising edges of the control-hot voltage V_(CH)are approximately equal to time periods T_(OS1), T_(LC)−T_(OS1), andT_(SP), respectively. At step 916, the microprocessor 360 determines ifthe first period T₁ is equal to the first offset time period T_(OS1)within the default tolerance ΔT_(OS), i.e.,if (T _(OS1) −ΔT _(OS))<T ₁≦(T _(OS1) +ΔT _(OS)).At step 918, the microprocessor 360 determines if the second period T₂is equal to the line cycle period T_(LC) minus the first offset timeperiod T_(OS1) within the widened tolerance ΔT_(OS-W), i.e.,if ([T _(LC) −T _(OS1) ]−ΔT _(OS-W))<T ₂≦([T _(LC) −T _(OS1) ]+ΔT_(OS-W)).At step 920, the microprocessor 360 determines if the third period T₃ isequal to the start symbol offset time period T_(START) within thedefault tolerance ΔT_(OS), i.e.,if (T _(START) −ΔT _(OS))<T ₃≦(T _(START) +ΔT _(OS)).If a start pattern was not received at step 916, 918, 920, themicroprocessor 360 sets the previous rising edge time t_(E-PREV) equalto the present rising edge time t_(E) at step 922. If the microprocessor360 is not presently receiving a digital message at step 924, thereceiving procedure 900 simply exits. If the microprocessor 360 receiveda start pattern at step 918, 920, 922, the microprocessor gets ready toreceive the data patterns of the digital message by clearing the RXbuffer at step 926 and setting a variable x to zero at step 928, beforethe receiving procedure 900 exits. The microprocessor 360 uses thevariable x to keep track of whether the next received edge will be areference edge (i.e., if the variable x is equal to zero) or a data edge(i.e., if the variable x is equal to one). Accordingly, themicroprocessor 360 will expect a reference edge during the nexthalf-cycle after setting the variable x equal to zero at step 928.

If the microprocessor 360 is presently receiving a digital message atstep 924 and the variable x equals zero at step 930, the microprocessor360 determines that the rising edge that was just received at step 910is a reference edge of a data pattern. Specifically, the microprocessor360 sets a reference edge time t_(REF) equal to the rising edge timet_(E) (from step 912) at step 932 and sets the variable x equal to oneat step 934, before the receiving procedure 900 exits. If themicroprocessor 360 is presently receiving a digital message at step 912and the variable x does not equal zero at step 930, the microprocessor360 determines that the rising edge that was just received at step 910is a data edge of a data pattern. The microprocessor 360 sets a measuredoffset time T_(M-OS) equal to rising edge time t_(E) minus the referenceedge time T_(REF) at step 936, i.e.,T _(M-OS) =t _(E) −t _(REF).The microprocessor 360 then executes a receive data procedure 1000 todetermine the bits of data that are encoded in the measured offset timeT_(M-OS) calculated at step 938, and the receiving procedure 900 exits.

FIG. 15 is a simplified flowchart of the receive data procedure 1000executed by the microprocessor 360 to determine the bits of data thatare encoded in the measured offset time period T_(M-OS) from thereceiving procedure 900. The microprocessor 360 uses a variable y tokeep track of which bits of the digital message are presently beingreceived, where a value of one for the variable y represents the firstbit and a value equal to the total number N_(DM) of bits of the digitalmessage represents the last bit of the digital message. Themicroprocessor 360 first determines if the measured offset time periodT_(M-OS) is equal to one of the offset time periods T_(OS1), T_(OS2),T_(OS3), T_(OS4) within the default tolerance ΔT_(OS). Specifically, ifthe measured offset time period T_(M-OS) is approximately equal to thefirst offset time T_(OS1) at step 1010, i.e.,if (T _(OS1) −ΔT _(OS))<T _(M-OS)≦(T _(OS1) +ΔT _(OS)),the microprocessor 360 sets the next two bits of the digital message inthe RX buffer RX[y+1,y] equal to “00” at step 1012. Similarly, if themeasured offset time period T_(M-OS) is approximately equal to thesecond offset time period T_(OS2) at step 1014, the third offset timeperiod T_(OS3) at step 1018, or the fourth offset time period T_(OS4) atstep 1022, the microprocessor 360 sets the next two bits of the digitalmessage in the RX buffer RX[y+1,y] equal to “01” at step 1016, to “10”at step 1020, or to “11” at step 1024, respectively.

If the variable y is not equal to the total number N_(DM) of bits of thedigital message minus one at step 1026, the microprocessor 360 increasesthe variable y by two at step 1028 and the receive data procedure 1000exits. If the variable y is equal to the total number N_(DM) of bits ofthe digital message minus one at step 1026 (i.e., the digital messagepresently being received is complete), the microprocessor 360 sets thevariable y to one at step 1030 and sets a message-received (MSG-RX) flagat step 1032, such that the microprocessor will process the receiveddigital message after the receive data procedure 1000 exits. Inaddition, the microprocessor 360 will begin to once again continuallymonitor the control-hot voltage V_(CH) to determine if the digitalballast controller has transmitted a start symbol.

FIG. 16 is a simple timing diagram of the control-hot voltage V_(CH)according to the second embodiment of the present invention. Accordingto the second embodiment of the present invention, each data pattern hasa half-cycle having a reference edge and a number N_(DP) of subsequenthalf-cycles having data edges. For example, there may be two data edgesper reference edge as shown in FIG. 16. The digital ballast controller120 is operable to generate a reference edge during a first half-cycleand then to generate data edges in each of the next two half-cycles.Accordingly, the digital ballast controller 120 is operable to transmitfour bits of data every three half-cycles (i.e., every 1.5 line cycles).The value of the data represented by the data edge in the secondhalf-cycle is dependent upon the offset time T_(OS) between the dataedge and the reference edge in the first half-cycle. The value of thedata represented by the data edge in the third half-cycle is dependentupon the offset time T_(OS) between the data edge in the thirdhalf-cycle and the time in the second half-cycle that is the firstoffset time period T_(OS1) from the reference edge in the firsthalf-cycle. In other words, the value of the data represented by thedata edge in the third half-cycle is dependent upon the offset timeperiod T_(OS) between the data edge in the third half-cycle and thereference edge in the first half-cycle minus the first offset timeperiod T_(OS1).

FIG. 17 is a simple timing diagram of the control-hot voltage V_(CH)showing the start pattern according to the second embodiment of thepresent invention. The digital ballast controller 120 is operable totransmit the start pattern by generating a reference edge during a firsthalf-cycle, rendering the controllably conductive device 210 conductivein a second subsequent half-cycle at the first offset period T_(OS1)from the reference edge in the first half-cycle (i.e., transmitting bits“00”), and then rendering the controllably conductive device conductiveafter the start symbol time period T_(START) after the firing time inthe previous half-cycle. As in the first embodiment, the start symboltime period T_(START) is unique from and longer than the offset timeperiods T_(OS1)−T_(OS4) used to transmit data to the digital dimmingballasts 110 (i.e., approximately 8.73 milliseconds). After transmittingthe start pattern, the digital ballast controller 120 is operable toimmediately begin transmitting data in the next line cycle by generatinga reference edge in the next half-cycle and data edges in the subsequenthalf-cycles as shown in FIG. 17.

FIG. 18 is a simplified flowchart of the timer interrupt procedure 1100that is executed by the microprocessor 214 of each digital ballastcontroller 120 to generate the reference and data edges of thetransmitted digital messages according to the second embodiment of thepresent invention. The timer interrupt procedure 1100 is executed by themicroprocessor 214 when the value of the timer equals the set interrupttime, and is very similar to the timer interrupt procedure 700 of thefirst embodiment. However, when the variable m is not equal to zero atstep 714 and is not equal to the number N_(DP) of data edges in eachdata pattern (i.e., two according to the second embodiment) at step1110, the microprocessor 214 sets the base time t₀ equal to the basetime t₀ from the previous half-cycle plus the first offset time periodT_(OS1) at step 1112, before increasing the variable m by one at step1114 and executing the data edge procedure 800. If the variable m is notequal to zero at step 714, but is equal to the number N_(DP) of dataedges in each data pattern at step 1110, the microprocessor 214 sets thevariable m to zero at step 720 and the timer interrupt procedure 1100exits.

FIG. 19 is a simplified flowchart of a receiving procedure 1200 executedby the microprocessor 360 of each digital dimming ballast 110periodically (e.g., once every half-cycle) to receive the digitalmessages from the digital ballast controller 120 according to the secondembodiment of the present invention. The receiving procedure 1200 isvery similar to the receiving procedure 900 of the first embodiment.However, according to the second embodiment, the microprocessor 360determines that a start pattern has been received by determining thatthe time periods T₁, T₂ between the rising edges in two consecutivehalf-cycles are equal to the first offset time period T_(OS1) and thestart symbol time period T_(START). Specifically, the microprocessor 360sets the first time period T₁ equal to the previous second time periodT₂ and sets the second time period T₂ equal to the rising edge timet_(E) minus a previous rising edge time t_(E-PREV) at step 1210, anddetermines that a start pattern has been received if the first period T₁is equal to the first offset time period T_(OS1) within the defaulttolerance ΔT_(OS) at step 1212 and the second period T₂ is equal to thestart symbol time period T_(START) within the default tolerance ΔT_(OS)at step 1214.

In addition, the microprocessor 360 calculates the measured offset timeT_(M-OS) in the second embodiment in dependence upon the variable x atstep 1216, i.e.,T _(M-OS)=(t _(TIMER) −t _(REF))−(x−1)·T _(OS1),before executing the receive data procedure 1000 to determine the bitsof data that are encoded in the measured offset time T_(M-OS). If thevariable x is not equal to the number N_(DP) of data edges in each datapattern at step 1218, the microprocessor 360 increments the variable xby one at step 1220 and the receiving procedure 1200 exits. If thevariable x is equal to the number N_(DP) of data edges in each datapattern at step 1218, the microprocessor 360 sets the variable x to zeroat step 1222 and the receiving procedure 1200 exits.

Alternatively, the digital ballast controller 120 could transmit and thedigital ballasts 110 could receive more than two data edges perreference edge using the timer interrupt procedure 1100 of FIG. 18 andthe receiving procedure of FIG. 19 if the number N_(DP) of data edges ineach data pattern is greater than two.

As previously mentioned, in some retrofit applications, the neutral wirecoupled to the neutral side of the AC power source 102 may not beavailable in the wallbox of the digital ballast controllers 120. FIG. 20is a simplified block diagram of a load control system 1300 comprising atwo-wire remote control device, e.g., a two-wire digital ballastcontroller 1320, that is adapted to be coupled in series electricalconnection between the AC power source 102 and the two-wire digitaldimming ballasts 110 without a connection to the neutral side of the ACpower source according to a third embodiment of the present invention.The load control system 1300 further comprises an active load circuit1390 that is coupled in parallel with the two-wire digital dimmingballasts 110 for providing a path for a charging current of a powersupply 1420 (FIG. 21) of the digital ballast controller 1320 to beconducted as will be described in greater detail below. For example, theactive load circuit 1390 may be housed in an enclosure and wired to thecircuit wiring 114 in one of the lighting fixtures with one of theballasts 110 of the load control system 1300. In addition, the activeload circuit 1390 could be included as part of the retrofit kit 180shown in FIG. 5. Alternatively, the active load circuit 1390 could beincluded in each of the ballasts 110 of the load control system 1300,e.g., coupled between the control-hot terminal CH and the neutralterminal N.

FIG. 21 is a simplified block diagram of the digital ballast controller1320 and the active load circuit 1390 according to the third embodimentof the present invention. The digital ballast controller 1320 is verysimilar to the digital ballast controller 120 of the first embodiment.The digital ballast controller 1320 of the third embodiment of thepresent invention is able to transmit digital messages to the digitaldimming ballasts using the communication techniques of the first andsecond embodiments. However, the digital ballast controller 1320comprises a zero-crossing detector 1416 that is coupled in parallel withthe controllably conductive device 210 for determining thezero-crossings of the AC power source 102. In addition, the power supply1420 is also coupled in parallel with the controllably conductive device210 and is operable to conduct a charging current I_(CHRG) to generate aDC supply voltage V_(CC) for powering the microprocessor 214, the memory218, and other low-voltage circuitry of the digital ballast controller1320. The power supply 1420 is operable to charge when the controllablyconductive device 210 is non-conductive at the beginning of eachhalf-cycle of the AC power source 102.

When the controllably conductive device 210 is non-conductive, the powersupply 1420 is coupled in series with the ballasts 110 across the ACpower source 102, such that the AC source voltage of the AC power source102 is split between the power supply and the ballasts, and themagnitude of the control-hot voltage V_(CH) across the ballasts dependsupon the relative impedance of the ballasts and the power supply. It isimportant to keep the magnitude of the control-hot voltage V_(CH) acrossthe ballasts 110 well below the rising threshold V_(TH-R) of the edgedetect circuit 380 of the ballasts during the time that the controllablyconductive device 210 is non-conductive. To meet this need, theimpedance between the control-hot terminal CH of the digital ballastcontroller 1320 and the neutral side of the AC power source 102 (i.e.,across the ballasts 110) must be lower than the impedance between thehot terminal H and the control-hot terminal CH of the digital ballastcontroller 1320 during the time that the controllably conductive device210 is non-conductive. Accordingly, the two-wire digital ballastcontroller 1320 of the third embodiment of the present inventioncomprises a current limit circuit 1430 in series electrical connectionwith the power supply 1420 to limit the magnitude of the chargingcurrent I_(CHRG) to be equal to or less than a first current limitI_(LIMIT1). The value of the first current limit I_(LIMIT1) depends onthe current requirements of the power supply 1420 and is chosen so thatthe power supply can fully recharge during the time that thecontrollably conductive device 210 is non-conductive each half-cycle.

The active load circuit 1390 conducts an active load current I_(AL)having a magnitude that is approximately equal to the magnitude of thecharging current I_(CHRG) of the power supply 1420 of the digitalballast controller 1320 when the controllably conductive device 210 isnon-conductive each half-cycle. The active load circuit 1390 comprises acurrent limit circuit 1490 that operates to ensure that the magnitude ofthe active load current I_(AL) is maintained equal to or less than asecond current limit I_(LIMIT2), which is selected to be greater thanthe first current limit I_(LIMIT1) of the digital ballast controller1320. For example, the magnitude of the second current limit I_(LIMIT2)may be approximately 1.2 times greater than the magnitude of the firstcurrent limit I_(LIMIT1). As long as the magnitude of the first currentlimit I_(LIMIT1) is lower than the magnitude of the second current limitI_(LIMIT2), the magnitude of the control-hot voltage V_(CH) across theballasts 110 (i.e., across the active load circuit 1390) will beapproximately zero volts during the time that the controllablyconductive device 210 is non-conductive each half-cycle.

When the controllably conductive device 210 becomes conductive, thecurrent available will be much greater than second current limitI_(LIMIT2), so the magnitude of the control-hot voltage V_(CH) acrossthe ballasts 110 will be able to increase up towards the magnitude ofthe AC source voltage of the AC power source 102. To prevent unnecessarypower dissipation, the active load circuit 1390 comprises a voltagethreshold circuit 1492 that is coupled in parallel with the currentlimit circuit 1490 and operates to disable the current limit circuitwhen the magnitude of the control-hot voltage V_(CH) across the activeload circuit 1390 exceeds an active-load-disable threshold V_(TH-ALD)(e.g., approximately 30 volts). The voltage threshold circuit 1492 has atime delay that requires the magnitude of the control-hot voltage V_(CH)across the active load circuit 1390 to be below the active-load-disablethreshold V_(TH-ALD) for a period of time, e.g. approximately 400microseconds, before re-enabling the current limit circuit 1490. Thistime delay significantly reduces the amount of current drawn by theactive load circuit 1390 near the end of each line half-cycle as themagnitude of the control-hot voltage V_(CH) approaches zero volts.

FIG. 22 is a simplified block diagram of a lighting control system 1500comprising a digital dimming ballast 1510 that is directly connected toone or more input devices, such as an occupancy sensor 1530 and adaylight sensor 1540, according to a fourth embodiment of the presentinvention. The occupancy sensor 1530 and the daylight sensor 1540 may bemounted to the lighting fixture in which the digital dimming ballast1510 is installed, and may be included as part of a retrofit kitincluding the digital dimming ballast 1510. The digital dimming ballast1510 is adapted to operate as a “mini-system” to control the intensityof the connected lamp 104 in response to the occupancy sensor 1530 andthe daylight sensor 1540. Dimming ballasts adapted to be directlyconnected to one or more input devices, such as sensors, are describedin greater detail in previously-referenced U.S. Pat. No. 7,619,539.

The digital dimming ballast 1510 is also operable to control theintensity of the connected lamp 104 in response to “broadcast” commandstransmitted by the digital ballast controller 120 via the control-hotvoltage V_(CH). The digital ballast controller 120 is operable totransmit the broadcast commands to the digital dimming ballast 1510 inresponse to RF signals 106 transmitted by a broadcast transmitter 1560of the load control system 1500. The broadcast transmitter 1560 isconnected to a network 1562 (e.g., a local area network or the Internet)via a network communication link 1564 (e.g., an Ethernet link) forreceiving the broadcast commands to transmit to the digital dimmingballast 1510. The broadcast commands may comprise, for example, at leastone of a timeclock command, a load shed command, or a demand responsecommand. The digital ballast controller 120 is operable to transmitinformation, such as the status and energy consumption of the controlledloads, back to the broadcast transmitter 1560, which may share theinformation with other control devices coupled on the network 1562. Thebroadcast transmitter 1560 is described in greater detail incommonly-assigned U.S. Provisional Patent Application No. 61/580,898,filed Dec. 28, 2011, entitled LOAD CONTROL SYSTEM HAVINGINDEPENDENTLY-CONTROLLED UNITS RESPONSIVE TO A BROADCAST TRANSMITTER,the entire disclosure of which is hereby incorporated by reference. Inaddition, the digital ballast controller 120 is also operable totransmit digital messages to the digital dimming ballast 1510 inresponse to the wireless occupancy sensor 130, the wireless daylightsensor 140, and the battery-powered remote control 150 (as in the firstembodiment).

FIG. 23 is a simple wiring diagram of a load control system 1600 havinga digital LED controller 1620 and a plurality of two-wire LED drivers1610 for controlling the intensity of respective LED light sources 1604(i.e., LED light engines) according to a fifth embodiment of the presentinvention. The digital LED controller 1620 of the fourth embodiment ofthe present invention is identical to the digital ballast controller 120of the first and second embodiments, and is able to transmit digitalmessages to the LED drivers 1610 using the communication techniquesdescribed above. In addition, the digital LED controller 1620 may have aconnection to the neutral side of the AC power source 102 as shown inFIG. 22 or may alternatively be a two-wire device as described in thethird embodiment of the present invention. Examples of LED drivers aredescribed in greater detail in co-pending, commonly-assigned U.S. patentapplication Ser. No. 12/813,908, filed Jun. 11, 2010, entitled LOADCONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE, the entiredisclosure of which is hereby incorporated by reference. According toanother alternate embodiment of the present invention, both digitaldimming ballasts 110 and LED drivers 1610 could be coupled to a singledigital ballast controller, such that the digital ballast controller isable to control multiple load types in a single load control system.

The digital ballast controllers 120, 1320 and LED controllers 1620 ofthe present invention generate the control-hot voltage V_(CH) such thatthe control-hot voltage resembles a forward phase-control voltage, i.e.,the controllably conductive device 210 is rendered conductive at afiring time each half-cycle and the data is encoded in time periodsbetween the timing edges (i.e., rising edges) of the control-hotvoltage. Alternatively, the digital ballast controllers 120, 1302 andLED controllers 1620 could render the controllably conductive device 210non-conductive at some time each half-cycle, such that the control-hotvoltage V_(CH) resembles a reverse phase-control voltage and the data isencoded in time periods between the timing edges (i.e., falling edges)of the control-hot voltage. In addition, the control-hot voltage V_(CH)could comprise a center phase-control voltage having both a rising edgetowards the beginning of a half-cycle and a falling edge towards the endof the half-cycle. When the control-hot voltage V_(CH) is a reversephase-control voltage or a center phase-control voltage, thecontrollably conductive device 210 may be implemented as, for example,two FETs in anti-series connection.

While the present invention has been described with reference to thesingle-phase electric power systems shown in FIGS. 1, 20, and 22, thecommunication techniques of the present invention could also be appliedto two-phase and three-phase electric power systems.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A load control system for controlling anelectrical load receiving power from an AC power source, the loadcontrol system comprising: a load control device for controlling theelectrical load; and a controller adapted to be coupled in serieselectrical connection between the AC power source and the load controldevice to conduct a load current from the AC power source to theelectrical load, the controller operable to produce a phase-controlvoltage is adapted to be received by the load control device, whereinthe phase-control voltage comprises an AC voltage that is characterizedby a conduction period for a portion of each half-cycle; wherein thecontroller is operable to transmit a digital message to the load controldevice for controlling the load by encoding digital information intiming edges of the phase-control voltage, the phase-control voltagehaving at least one timing edge in each half-cycle of the AC powersource when the controller is transmitting the digital message to theload control device.
 2. The load control system of claim 1, wherein thephase-control voltage produced by the controller has a number ofsequential data patterns, each data pattern having a first timing edgeat a predetermined reference edge time during a first half-cycle and asecond timing edge at a data edge time during a second subsequenthalf-cycle, such that an offset time period exists between the referenceedge time and the data edge time of each data pattern, the controlleroperable to transmit the digital message to the load control device bycontrolling the offset time period in each of the sequential datapatterns.
 3. The load control system of claim 2, wherein the controlleris operable to transmit the digital message to the load control deviceby adjusting the offset time period between the reference edge timeduring the first half-cycle and the data edge time during the secondhalf-cycle to be one of a plurality of possible predetermined offsettime periods.
 4. The load control system of claim 3, wherein thecontroller is operable to transmit the digital message to the loadcontrol device by adjusting the offset time period of each data patternto one of four possible predetermined offset time periods.
 5. The loadcontrol system of claim 4, wherein the controller is operable to controleach data pattern of the phase-control voltage to have a third timingedge at a data edge time during a third half-cycle immediately followingthe second half-cycle, such that a second offset time period existsbetween the reference edge time during the first half-cycle and the dataedge time during the third half-cycle.
 6. The load control system ofclaim 5, wherein the second offset time period between the referenceedge time during the first half-cycle and the data edge time during thethird half-cycle may be controlled to one of four possible predeterminedoffset time periods.
 7. The load control system of claim 6, wherein thecontroller is operable to transmit four bits of data per 1.5 linecycles.
 8. The load control system of claim 4, wherein the controller isoperable to control the phase-control voltage to have a third timingedge at a second reference edge time during a third half-cycleimmediately following the second half-cycle and to have a fourth timingedge at a second data edge time during a fourth subsequent half-cycle,such that a second offset time period exists between the secondreference edge time and the second data edge time.
 9. The load controlsystem of claim 8, wherein the controller is operable to transmit twobits of data per line cycle.
 10. The load control system of claim 3,wherein the controller is operable to transmit the digital message tothe load control device over a predetermined number of consecutive linecycles.
 11. The load control system of claim 10, wherein the controlleris operable to transmit a start symbol to begin transmitting a digitalmessage by controlling the phase-control voltage to have a third timingedge at a first start symbol edge time during a third half-cycle and afourth timing edge at a second start symbol edge time during a fourthsubsequent half-cycle, such that a start symbol offset time periodexists between the first start symbol edge time and the second startsymbol edge time, the third and fourth half-cycles occurring before thefirst and second half-cycles, the start symbol offset time period notbeing equal to any of the possible offset time periods that may existbetween the reference edge time during the first half-cycle and the dataedge time during the second half-cycle.
 12. The load control system ofclaim 11, wherein the start symbol offset time period is longer than thepossible offset time periods that may exist between the reference edgetime during the first half-cycle and the data edge time during thesecond half-cycle.
 13. The load control system of claim 11, wherein thecontroller is operable to interrupt a first digital message that isbeing transmitted in order to transmit a second digital message to theload control devices by transmitting the start symbol before the end ofthe first digital message.
 14. The load control system of claim 2,wherein the digital message transmitted by the controller comprises apredetermined number of bits, such that the digital message istransmitted to the load control device over a predetermined number ofconsecutive line cycles.
 15. The load control system of claim 14,wherein the digital message transmitted by the controller indicates acontrol channel, the load control device operable to decide whether torespond to the digital message or not in response to the control channelof the digital message.
 16. The load control system of claim 15, whereinthe digital message transmitted by the controller further comprisescommand data and a command type specifying how the load control deviceshould respond to the command data.
 17. The load control system of claim16, wherein the digital message transmitted by the controller furthercomprises a predetermined number of error detect bits to allow the loadcontrol device to determine if an error occurred during transmission andreception of the digital message.
 18. The load control system of claim17, wherein the digital message transmitted by the controller furthercomprises a start symbol at the beginning.
 19. The load control systemof claim 1, wherein the controller comprises a two-wire device.
 20. Theload control system of claim 19, wherein the controller comprises acontrollably conductive device adapted to be coupled in serieselectrical connection between the AC power source and the electricalload for generating the phase-control voltage.
 21. The load controlsystem of claim 20, wherein the controller comprises a power supplycoupled in parallel electrical connection with the controllablyconductive device for conducting a charging current when thecontrollably conductive device is non-conductive to generate a DC supplyvoltage.
 22. The load control system of claim 21, further comprising: anactive load circuit coupled in parallel electrical connection with theload control device for providing a path for the charging current of thepower supply of the controller, the active load circuit operable toconduct an active load current having a magnitude approximately equal tothe magnitude of the charging current of the power supply of thecontroller when the controllably conductive device is non-conductive.23. The load control system of claim 22, wherein the controllercomprises a current limit circuit coupled in series with the powersupply for limiting the magnitude of the charging current to a firstcurrent limit.
 24. The load control system of claim 22, wherein theactive load circuit comprises a current limit circuit operable to limitthe magnitude of the active load current to a second current limitgreater than the first current limit, and a voltage threshold circuitoperable to disable the current limit circuit when the magnitude of thevoltage across the active load circuit exceeds a voltage threshold. 25.The load control system of claim 20, wherein the controllably conductivedevice is operable to conduct a load current from the AC power source tothe electrical load.
 26. The load control system of claim 1, furthercomprising: an input device operable to transmit a control signal to thecontroller; wherein the controller is operable to generate thephase-control voltage to transmit the digital message to the loadcontrol device in response to the control signal received from the inputdevice.
 27. The load control system of claim 26, wherein the inputdevice comprises an RF transmitter operable to transmit an RF signal tothe controller.
 28. The load control system of claim 1, wherein theelectrical load receives power from the AC power source over an existingpower wiring, the controller adapted to be coupled in series electricalconnection between the AC power source and the load control device viathe existing power wiring, such that the controller is operable totransmit the digital message to the load control device via the existingpower wiring.
 29. The load control system of claim 1, wherein thecontroller is adapted to be wall-mounted to a single-gang or multi-gangelectrical wallbox, mounted inside an electrical wallbox, mounted to ajunction box, mounted in an electrical panel, mounted to a DIN rail, ormounted to a ceiling.
 30. The load control system of claim 1, whereinthe load control device comprises one of: a dimming circuit forcontrolling the intensity of a lighting load; an electronic dimmingballast for driving a gas-discharge lamp; a light-emitting diode driverfor driving a light-emitting diode light source; a screw-in luminaireincluding a dimmer circuit and an incandescent or halogen lamp; ascrew-in luminaire including a ballast and a compact fluorescent lamp; ascrew-in luminaire including an LED driver and an LED light source; anelectronic switch, controllable circuit breaker, or other switchingdevice for turning an appliance on and off; a plug-in load controldevice, controllable receptacle, or controllable power strip forcontrolling one or more plug-in loads; a motor control unit forcontrolling a motor load, such as a ceiling fan or an exhaust fan; adrive unit for controlling a motorized window treatment or a projectionscreen; motorized interior or exterior shutters; a thermostat for aheating and/or cooling system; a temperature control device forcontrolling a setpoint temperature of an HVAC system; an airconditioner; a compressor; an electric baseboard heater controller; acontrollable damper; a humidity control unit; a dehumidifier; a waterheater; a pool pump; a TV or computer monitor; an audio system oramplifier; a generator; an electric charger; electric vehicle charger,and an alternative energy controller.
 31. The load control system ofclaim 1, wherein the controller has a direct connection to the neutralside of the AC power source.
 32. The load control system of claim 1,wherein the phase-control voltage has at least one timing edge in eachhalf-cycle of the AC power source when the controller is transmitting adigital message to the load control device and when the controller isnot transmitting a digital message to the load control device.
 33. Theload control system of claim 1, wherein the phase-control voltage doesnot have at least one timing edge in each half-cycle of the AC powersource when the controller is not transmitting a digital message to theload control device.
 34. A method of transmitting a digital message froma controller to a load control device for controlling an electrical loadreceiving power from an AC power source, the method comprising: thecontroller generating a phase-control voltage, wherein the phase-controlvoltage comprises an AC voltage that is characterized by a conductionperiod for a portion of each half-cycle; the controller transmitting thedigital message by encoding digital information in the timing edges ofthe phase-control voltage, the phase-control voltage having at least onetiming edge in each half-cycle of the AC power source when thecontroller is transmitting the digital message; the load control devicereceiving the phase-control voltage from the controller; and the loadcontrol device controlling the load in response to the digitalinformation encoded in the timing edges of the phase-control voltage.35. The method of claim 34, wherein the step of the controllergenerating a phase-control voltage comprises the controller generating aphase-control voltage having a number of sequential data patterns, eachdata pattern having a first timing edge at a predetermined referenceedge time during a first half-cycle and a second timing edge at a dataedge time during a second subsequent half-cycle, such that an offsettime period exists between the reference edge time and the data edgetime of each data pattern.
 36. The method of claim 35, wherein the stepof the controller transmitting the digital message comprises controllingthe offset time period in each of the sequential data patterns.
 37. Themethod of claim 36, wherein the step of the controller transmitting thedigital message comprises adjusting the offset time period of each datapattern to be one of a plurality of possible predetermined offset timeperiods.
 38. The method of claim 37, wherein the step of the controllertransmitting the digital message comprises adjusting the offset timeperiod of each data pattern to one of four possible predetermined offsettime periods.
 39. The method of claim 38, wherein the step of thecontroller generating a phase-control voltage comprises the controllergenerating a third timing edge of the phase-control voltage at a dataedge time during a third half-cycle immediately following the secondhalf-cycle of the data pattern, such that a second offset time periodexists between the reference edge time during the first half-cycle andthe data edge time during the third half-cycle.
 40. The method of claim38, wherein the step of the controller generating a phase-controlvoltage comprises the controller generating a third timing edge of thephase-control voltage at a second reference edge time during a thirdhalf-cycle immediately following the second half-cycle and generating afourth timing edge of the phase-control voltage at a second data edgetime during a fourth subsequent half-cycle, such that a second offsettime period exists between the second reference edge time and the seconddata edge time.
 41. The method of claim 37, wherein the step of thecontroller transmitting the digital message comprises: the controllertransmitting the digital message to the load control device over apredetermined number of consecutive line cycles; and the controllertransmitting a start symbol to begin transmitting the digital message bycontrolling the phase-control voltage to have a third timing edge at afirst start symbol edge time during a third half-cycle and a fourthtiming edge at a second start symbol edge time during a fourthsubsequent half-cycle, such that a start symbol offset time periodexists between the first start symbol edge time and the second startsymbol edge time, the third and fourth half-cycles occurring before thefirst and second half-cycles, the start symbol offset time period notbeing equal to any of the possible offset time periods that may existbetween the reference edge time during the first half-cycle and the dataedge time during the second half-cycle.
 42. The method of claim 41,wherein the start symbol offset time period is longer than the possibleoffset time periods that may exist between the reference edge timeduring the first half-cycle and the data edge time during the secondhalf-cycle.
 43. The method of claim 41, further comprising: thecontroller interrupting a first digital message that is beingtransmitted in order to transmit a second digital message to the loadcontrol devices by transmitting the start symbol before the end of thefirst digital message.
 44. The method of claim 34, further comprising:transmitting an RF signal to the controller from an RF transmitter;wherein the step of the controller transmitting the digital messagecomprises the controller transmitting the digital message to the loadcontrol device in response to the RF signal received from the RFtransmitter.
 45. A load control system for controlling an electricalload receiving power from an AC power source, the load control systemcomprising: a load control device adapted to be coupled to theelectrical load for controlling the power delivered to the electricalload; and a controller adapted to be coupled in series electricalconnection between the AC power source and the load control device, thecontroller operable to produce a phase-control voltage that is adaptedto be received by the load control device; wherein the phase-controlvoltage produced by the controller is characterized by a number ofsequential data patterns, each data pattern having a first timing edgeat a predetermined reference edge time during a first half-cycle and asecond timing edge at a data edge time during a second subsequenthalf-cycle, such that an offset time period exists between the referenceedge time and the data edge time of each data pattern, the controlleroperable to transmit a digital message to the load control device forcontrolling the power delivered to the load by controlling the offsettime period in each of the sequential data patterns.
 46. The loadcontrol system of claim 45, wherein the controller is operable totransmit the digital message to the load control device by adjusting theoffset time period between the reference edge time during the firsthalf-cycle and the data edge time during the second half-cycle to be oneof a plurality of possible predetermined offset time periods.
 47. Theload control system of claim 46, wherein the controller is operable totransmit the digital message to the load control device by adjusting theoffset time period of each data pattern to one of four possiblepredetermined offset time periods.
 48. The load control system of claim47, wherein the controller is operable to control each data pattern ofthe phase-control voltage to have a third timing edge at a data edgetime during a third half-cycle immediately following the secondhalf-cycle, such that a second offset time period exists between thereference edge time during the first half-cycle and the data edge timeduring the third half-cycle.
 49. The load control system of claim 48,wherein the second offset time period between the reference edge timeduring the first half-cycle and the data edge time during the thirdhalf-cycle may be controlled to one of four possible predeterminedoffset time periods.
 50. The load control system of claim 49, whereinthe controller is operable to transmit four bits of data per 1.5 linecycles.
 51. The load control system of claim 47, wherein the controlleris operable to control the phase-control voltage to have a third timingedge at a second reference edge time during a third half-cycleimmediately following the second half-cycle and to have a fourth timingedge at a second data edge time during a fourth subsequent half-cycle,such that a second offset time period exists between the secondreference edge time and the second data edge time.
 52. The load controlsystem of claim 51, wherein the controller is operable to transmit twobits of data per line cycle.
 53. The load control system of claim 46,wherein the controller is operable to transmit the digital message tothe load control device over a predetermined number of consecutive linecycles.
 54. The load control system of claim 53, wherein the controlleris operable to transmit a start symbol to begin transmitting a digitalmessage by controlling the phase-control voltage to have a third timingedge at a first start symbol edge time during a third half-cycle and afourth timing edge at a second start symbol edge time during a fourthsubsequent half-cycle, such that a start symbol offset time periodexists between the first start symbol edge time and the second startsymbol edge time, the third and fourth half-cycles occurring before thefirst and second half-cycles, the start symbol offset time period notbeing equal to any of the possible offset time periods that may existbetween the reference edge time during the first half-cycle and the dataedge time during the second half-cycle.
 55. The load control system ofclaim 54, wherein the start symbol offset time period is longer than thepossible offset time periods that may exist between the reference edgetime during the first half-cycle and the data edge time during thesecond half-cycle.
 56. The load control system of claim 54, wherein thecontroller is operable to interrupt a first digital message that isbeing transmitted in order to transmit a second digital message to theload control devices by transmitting the start symbol before the end ofthe first digital message.
 57. The load control system of claim 45,wherein the digital message transmitted by the controller comprises apredetermined number of bits, such that the digital message istransmitted to the load control device over a predetermined number ofconsecutive line cycles.
 58. The load control system of claim 57,wherein the digital message transmitted by the controller indicates acontrol channel, the load control device operable to decide whether torespond to the digital message or not in response to the control channelof the digital message.
 59. The load control system of claim 58, whereinthe digital message transmitted by the controller further comprisescommand data and a command type specifying how the load control deviceshould respond to the command data.
 60. The load control system of claim59, wherein the digital message transmitted by the controller furthercomprises a predetermined number of error detect bits to allow the loadcontrol device to determine if an error occurred during transmission andreception of the digital message.
 61. The load control system of claim60, wherein the digital message transmitted by the controller furthercomprises a start symbol at the beginning.
 62. The load control systemof claim 45, wherein the controller comprises a two-wire device.
 63. Theload control system of claim 62, wherein the controller comprises acontrollably conductive device adapted to be coupled in serieselectrical connection between the AC power source and the electricalload for generating the phase-control voltage.
 64. The load controlsystem of claim 63, wherein the controller comprises a power supplycoupled in parallel electrical connection with the controllablyconductive device for conducting a charging current when thecontrollably conductive device is non-conductive to generate a DC supplyvoltage.
 65. The load control system of claim 64, further comprising: anactive load circuit coupled in parallel electrical connection with theload control device for providing a path for the charging current of thepower supply of the controller, the active load circuit operable toconduct an active load current having a magnitude approximately equal tothe magnitude of the charging current of the power supply of thecontroller when the controllably conductive device is non-conductive.66. The load control system of claim 65, wherein the controllercomprises a current limit circuit coupled in series with the powersupply for limiting the magnitude of the charging current to a firstcurrent limit.
 67. The load control system of claim 65, wherein theactive load circuit comprises a current limit circuit operable to limitthe magnitude of the active load current to a second current limitgreater than the first current limit, and a voltage threshold circuitoperable to disable the current limit circuit when the magnitude of thevoltage across the active load circuit exceeds a voltage threshold. 68.The load control system of claim 63, wherein the controllably conductivedevice is operable to conduct a load current from the AC power source tothe electrical load.
 69. The load control system of claim 45, furthercomprising: an input device operable to transmit a control signal to thecontroller; wherein the controller is operable to generate thephase-control voltage to transmit the digital message to the loadcontrol device in response to the control signal received from the inputdevice.
 70. The load control system of claim 69, wherein the inputdevice comprises an RF transmitter operable to transmit an RF signal tothe controller.
 71. The load control system of claim 45, wherein theelectrical load receives power from the AC power source over an existingpower wiring, the controller adapted to be coupled in series electricalconnection between the AC power source and the load control device viathe existing power wiring, such that the controller is operable totransmit the digital message to the load control device via the existingpower wiring.
 72. The load control system of claim 45, wherein thecontroller is adapted to be wall-mounted to a single-gang or multi-gangelectrical wallbox, mounted inside an electrical wallbox, mounted to ajunction box, mounted in an electrical panel, mounted to a DIN rail, ormounted to a ceiling.
 73. The load control system of claim 45, whereinthe load control device comprises one of: a dimming circuit forcontrolling the intensity of a lighting load; an electronic dimmingballast for driving a gas-discharge lamp; a light-emitting diode driverfor driving a light-emitting diode light source; a screw-in luminaireincluding a dimmer circuit and an incandescent or halogen lamp; ascrew-in luminaire including a ballast and a compact fluorescent lamp; ascrew-in luminaire including an LED driver and an LED light source; anelectronic switch, controllable circuit breaker, or other switchingdevice for turning an appliance on and off; a plug-in load controldevice, controllable receptacle, or controllable power strip forcontrolling one or more plug-in loads; a motor control unit forcontrolling a motor load, such as a ceiling fan or an exhaust fan; adrive unit for controlling a motorized window treatment or a projectionscreen; motorized interior or exterior shutters; a thermostat for aheating and/or cooling system; a temperature control device forcontrolling a setpoint temperature of an HVAC system; an airconditioner; a compressor; an electric baseboard heater controller; acontrollable damper; a humidity control unit; a dehumidifier; a waterheater; a pool pump; a TV or computer monitor; an audio system oramplifier; a generator; an electric charger; electric vehicle charger,and an alternative energy controller.
 74. The load control system ofclaim 45, wherein the phase-control voltage has at least one timing edgein each half-cycle of the AC power source when the controller istransmitting a digital message to the load control device and when thecontroller is not transmitting a digital message to the load controldevice.
 75. The load control system of claim 45, wherein thephase-control voltage does not have at least one timing edge in eachhalf-cycle of the AC power source when the controller is nottransmitting a digital message to the load control device.
 76. A loadcontrol system for controlling a plurality of electrical loads receivingpower from an AC power source via a power wiring, the load controlsystem comprising: a plurality of load control devices adapted to becoupled in parallel with each other and operable to control respectiveelectrical loads; and a controller adapted to be coupled in serieselectrical connection between the AC power source and the parallelcombination of the load control devices via the power wiring, thecontroller operable to produce a phase-control voltage that is receivedby the load control devices, the controller operable to transmit adigital message to the load control devices via the power wiring byencoding digital information in the timing edges of the phase-controlvoltage, the phase-control voltage having at least one timing edge ineach half-cycle of the AC power source when the controller istransmitting the digital message to the load control devices; whereineach of the digital messages includes data representing at least one ofa plurality of control channels, the at least one of the controlchannels indicating which of the load control devices should react tothe digital message.
 77. The load control system of claim 76, whereinthe controller comprises a controllably conductive device adapted toconduct a total load current of the electrical loads.
 78. The loadcontrol system of claim 77, wherein the plurality of load controldevices comprises a non-dim load control device adapted to be coupled toone or more of the electrical loads for controlling the power deliveredto the loads, the non-dim load control device not responsive to thedigital message transmitted by the controller, the controller operableto turn off the loads connected to the non-dim load control device byrendering the controllably conductive device non-conductive for aplurality of consecutive half-cycles.
 79. The load control system ofclaim 76, wherein a first one of the load control devices comprises oneof a plurality of possible load control devices including: a dimmingcircuit for controlling the intensity of a lighting load; a dimmingballast for driving a gas-discharge lamp; a light-emitting diode driverfor driving a light-emitting diode light source; a screw-in luminaireincluding a dimmer circuit and an incandescent or halogen lamp; ascrew-in luminaire including a ballast and a compact fluorescent lamp; ascrew-in luminaire including an LED driver and an LED light source; anelectronic switch, controllable circuit breaker, or other switchingdevice for turning an appliance on and off; a plug-in load controldevice, controllable receptacle, or controllable power strip forcontrolling one or more plug-in loads; a motor control unit forcontrolling a motor load, such as a ceiling fan or an exhaust fan; adrive unit for controlling a motorized window treatment or a projectionscreen; motorized interior or exterior shutters; a thermostat for aheating and/or cooling system; a temperature control device forcontrolling a setpoint temperature of an HVAC system; an airconditioner; a compressor; an electric baseboard heater controller; acontrollable damper; a humidity control unit; a dehumidifier; a waterheater; a pool pump; a TV or computer monitor; an audio system oramplifier; a generator; an electric charger; electric vehicle charger;and an alternative energy controller.
 80. The load control system ofclaim 79, wherein a second one of the load control devices comprises adifferent one of the plurality of possible load control devices.
 81. Aload control system for controlling a plurality of electrical loadsreceiving power from an AC power source via a power wiring, the loadcontrol system comprising: a plurality of load control devices coupledin parallel with each other and operable to control respectiveelectrical loads; and a controller adapted to be coupled in serieselectrical connection between the AC power source and the parallelcombination of the load control devices via the power wiring, thecontroller operable to produce a phase-control voltage that is adaptedto be received by the load control devices, the phase-control voltagecharacterized by a number of sequential data patterns, each data patternhaving a first timing edge at a predetermined reference edge time duringa first half-cycle and a second timing edge at a data edge time during asecond subsequent half-cycle, such that an offset time period existsbetween the reference edge time and the data edge time of each datapattern, the controller operable to transmit a digital message to theload control devices via the power wiring by controlling the offset timeperiod in each of the sequential data patterns; wherein the digitalmessage includes data representing at least one of a plurality ofcontrol channels, the at least one of the control channels indicatingwhich of the load control devices should react to the digital message.82. A load control system for controlling an electrical load receivingpower from an AC power source via a power wiring, the system comprising:a load control device for controlling the electrical load; a controlleradapted to be coupled in series electrical connection between the ACpower source and the load control device to conduct a load current fromthe AC power source to the electrical load, the controller operable toproduce a phase-control voltage that is received by the load controldevice, wherein the phase-control voltage comprises an AC voltage thatis characterized by a conduction period for a portion of eachhalf-cycle; and an input device operable to transmit a control signal tothe controller; wherein the controller is operable to transmit a digitalmessage to the load control device for controlling the load by encodingdigital information in timing edges of the phase-control voltage inresponse to the control signal received from the input device, thephase-control voltage having at least one timing edge in each half-cycleof the AC power source when the controller is transmitting the digitalmessage to the load control device.
 83. The load control system of claim82, wherein the input device comprises a wireless transmitter operableto transmit a wireless signal to the controller.
 84. The load controlsystem of claim 83, wherein the wireless transmitter comprises an RFtransmitter operable to transmit RF signals to the controller inaccordance with a predefined RF communication protocol.
 85. The loadcontrol system of claim 84, wherein the predefined RF communicationprotocol comprises one of: Clear Connect, WiFi, Zigbee, Z-wave, KNX-RF,and EnOcean Radio protocols.
 86. The load control system of claim 83,wherein the wireless transmitter is operable to transmit the wirelesssignal via one of a plurality of wireless mediums, the wireless mediumcomprising one of radio-frequency signals, infrared signals, and sound.87. The load control system of claim 82, wherein the input devicecomprises a wired transmitter operable to transmit control signals tothe controller via a wired control link.
 88. The load control system ofclaim 87, wherein the wired transmitter is operable to transmit thecontrol signals to the controller in accordance with a predefinedcommunication protocol comprising one of: Ethernet, IP, XML, WebServices, QS, DMX, BACnet, Modbus, LonWorks, and KNX protocols.
 89. Theload control system of claim 87, wherein the wired control linkcomprises one of a serial digital communication link, an RS-485communication link, an RS-232 communication link, a DALI communicationlink, an Ecosystem communication link, an Ethernet communication link,and analog communication link.
 90. The load control system of claim 87,wherein the wired transmitter is operable to produce one of aline-voltage control signal, a phase-control signal, a 0-10V controlsignal, and a contact closure output control signal.
 91. The loadcontrol system of claim 82, further comprising: a second input devicedirectly connected to the load control device, the load control deviceoperable to control the electrical load in response to a second controlsignal transmitted by the second input device.
 92. The load controlsystem of claim 91, wherein the second input device comprises one of anoccupancy sensor, a vacancy sensor, and a daylight sensor.
 93. The loadcontrol system of claim 82, wherein the input device comprises one of:an occupancy sensor, a vacancy sensor, a daylight sensor, a temperaturesensor, a humidity sensor, a security sensor, a proximity sensor, akeypad, a battery-powered remote control, a key fob, a personal digitalassistant, a cell phone, a smart phone, a tablet, a personal computer, atimeclock, an audio-visual control, a safety device, a fire protectiondevice, a water protection device, and a medical emergency device. 94.The load control system of claim 83, wherein the input device comprisesa central control transmitter, the wireless signal transmitted by thecentral control transmitter comprising one of: a timeclock command, aload shed command, a demand response command, a peak demand command, ortime-of-day pricing information.
 95. The load control system of claim82, wherein the controller comprises an actuator adapted to be actuatedby a user, the controller operable to transmit the digital message tothe load control device for controlling the load in response to anactuation of the actuator.
 96. A load control system for controlling aplurality of electrical loads receiving power from an AC power sourcevia a power wiring, the load control system comprising: a plurality ofload control devices adapted to be coupled in parallel with each otherand operable to control respective electrical loads; a controlleradapted to be coupled in series electrical connection between the ACpower source and the parallel combination of the load control devicesvia the power wiring to conduct a load current from the AC power sourceto the plurality of electrical loads, the controller operable to producea phase-control voltage that is received by the load control device,wherein the phase-control voltage comprises an AC voltage that ischaracterized by a conduction period for a portion of each half-cycle;and a plurality of input devices operable to transmit control signals tothe controller, wherein a first set of input devices is associated witha first control channel of a plurality of control channels, and a secondset of input devices is associated with a second control channel of theplurality of control channels; and wherein the controller is operable totransmit a digital message to the load control device via the powerwiring by encoding digital information in timing edges of thephase-control voltage in response to a control signal received from oneof the input devices, the digital message including data representing atleast one of the plurality of control channels that is dependent uponthe input device from which the control signal was received.
 97. Theload control system of claim 96, wherein the at least one of the controlchannels indicates which of the load control devices should react to thedigital message.
 98. The load control system of claim 97, wherein eachof the load control devices is operable to control the respective loadin response to a command of a received digital message if the controlchannel of the received digital message is stored in a memory of theload control device.
 99. The load control system of claim 98, whereineach load control device comprises a DIP switch for selecting thecontrol channel.
 100. The load control system of claim 98, wherein eachload control device is operable to select the control channel inresponse to one or more digital messages received from the controller.101. The load control system of claim 96, wherein the first set of inputdevices comprises one of a plurality of possible input devicesincluding: an occupancy sensor, a vacancy sensor, a daylight sensor, atemperature sensor, a humidity sensor, a security sensor, a proximitysensor, a keypad, a battery-powered remote control, a key fob, apersonal digital assistant, a cell phone, a smart phone, a tablet, apersonal computer, a timeclock, an audio-visual control, a safetydevice, a fire protection device, a water protection device, a medicalemergency device, and a central control transmitter.
 102. The loadcontrol system of claim 101, wherein the second set of input devicescomprises a different one of the plurality of possible input devices.103. A load control system for controlling an electrical load receivingpower from an AC power source via a power wiring, the system comprising:a load control device for controlling the electrical load; and acontroller comprising a controllably conductive device adapted to becoupled in series electrical connection between the AC power source andthe load control device via the power wiring, such that the controllablyconductive device is operable to conduct a load current from the ACpower source to the electrical load, the controller operable to producea phase-control voltage that is received by the load control device,such that the phase-control voltage only exists on the power wiringbetween the controller and the load control device and the phase-controlvoltage does not interfere with other devices coupled to the AC powersource, wherein the phase-control voltage comprises an AC voltage thatis characterized by a conduction period for a portion of eachhalf-cycle; wherein the controller is operable to transmit a digitalmessage to the load control device for controlling the load by encodingdigital information in timing edges of the phase-control voltage, thephase-control voltage having at least one timing edge in each half-cycleof the AC power source when the controller is transmitting the digitalmessage to the load control device.
 104. The load control system ofclaim 103, wherein the controllably conductive device of the controllercomprises a bidirectional semiconductor switch.
 105. The load controlsystem of claim 104, wherein the bidirectional semiconductor switchcomprises one of: a triac, a FET in a rectifier bridge, two FETs inanti-series connection, and one or more IGBTs.
 106. The load controlsystem of claim 103, wherein the phase-control voltage is not degradedby a reactive element coupled in parallel electrical connection with theAC power source.
 107. A load control system for controlling the powerdelivered to a plurality of electrical loads, the load control systemcoupled to an AC power source, the load control system comprising: aplurality of load control devices, each of the load control devicesadapted to be coupled to one or more of the electrical loads forcontrolling the power delivered to the loads, the plurality of loadcontrol devices comprising a first load control device and a second loadcontrol device adapted to be coupled in parallel electrical connection,the first and second load control devices adapted to be coupled to afirst circuit wiring for receiving power from the AC power source, theplurality of load control devices further comprising a third loadcontrol device and a fourth load control device adapted to be coupled inparallel electrical connection, the third and fourth load controldevices adapted to be coupled to a second circuit wiring for receivingpower from the AC power source; a plurality of controllers, theplurality of controllers comprising a first controller adapted to becoupled to the first circuit wiring in series electrical connectionbetween the AC power source and the first and second load controldevices, the plurality of controllers further comprising a secondcontroller adapted to be coupled to the second circuit wiring in serieselectrical connection between the AC power source and the third andfourth load control devices, the first and third load control devicescharacterized with a first channel and the second and fourth loadcontrol devices characterized with a second channel; and an input deviceadapted to transmit control signals directly to the first and secondcontrollers; wherein the first controller is operable to transmit afirst digital message to the first and second load control devices viathe first circuit wiring and the second controller is operable totransmit a second digital message to the third and fourth load controldevices via the second circuit wiring in response to the control signalsreceived from the input device, the first and second digital messagesindicating the first channel, such that the first and third load controldevices are responsive to the first and second digital messagestransmitted by the first and second controllers in response to thecontrol signals received from the input device.
 108. The load controlsystem of claim 107, wherein the first and second controllers areoperable to produce phase-control voltages that are received by therespective load control devices, the first and second controllersoperable to transmit the first and second digital messages to the loadcontrol devices for controlling the respective loads by encoding digitalinformation in timing edges of the phase-control voltages.
 109. The loadcontrol system of claim 108, wherein the phase-control voltages producedby the first and second controllers each have at least one timing edgein each half-cycle of the AC power source when the first and secondcontrollers, respectively, are transmitting the first and second digitalmessages to the respective load control devices.
 110. The load controlsystem of claim 108, wherein the phase-control voltages generated by thefirst and second controllers each have a number of sequential datapatterns, each data pattern having a first timing edge at apredetermined reference edge time during a first half-cycle and a secondtiming edge at a data edge time during a second subsequent half-cycle,such that an offset time period exists between the reference edge timeand the data edge time of each data pattern, the first and secondcontrollers operable to transmit the first and second digital messagesto the respective load control devices by controlling the offset timeperiod in each of the sequential data patterns.
 111. The load controlsystem of claim 107, further comprising: a second input device adaptedto transmit control signals directly to the first and secondcontrollers; wherein the first and second controllers are operable totransmit third and fourth digital messages both indicating the secondchannel to the load control devices in response to receiving the controlsignals from the second input device, the second and fourth load controldevices responsive to the third and fourth digital messages transmittedby the first and second controllers in response to the control signalstransmitted by the second input device.
 112. The load control system ofclaim 111, wherein each load control device comprises a DIP switch forselecting the channel.
 113. The load control system of claim 107,wherein each of the controllers comprises a controllably conductivedevice adapted to conduct a total load current of the electrical loadscoupled to the respective circuit wiring.
 114. The load control systemof claim 113, wherein each of the controllers is operable to render thecontrollably conductive device non-conductive for a plurality ofconsecutive half-cycles if each of the electrical loads coupled to therespective circuit wiring should be off.
 115. The load control system ofclaim 113, wherein the plurality of load control devices comprises afifth load control device adapted to be coupled to one or more of theelectrical loads for controlling the power delivered to the loads, thefifth load control device adapted to be coupled to the first circuitwiring in parallel electrical connection with the first and second loadcontrol devices, the fifth load control device comprising a non-dim loadcontrol device that is not responsive to the first and second digitalmessages transmitted by the first controller to the first and secondload control devices, the first controller operable to turn off theloads connected to the fifth load control device by rendering thecontrollably conductive device non-conductive for a plurality ofconsecutive half-cycles.
 116. The load control system of claim 107,wherein the first load control device comprises one of a plurality ofpossible load control devices including: a dimming circuit forcontrolling the intensity of a lighting load; a dimming ballast fordriving a gas-discharge lamp; a light-emitting diode driver for drivinga light-emitting diode light source; a screw-in luminaire including adimmer circuit and an incandescent or halogen lamp; a screw-in luminaireincluding a ballast and a compact fluorescent lamp; a screw-in luminaireincluding an LED driver and an LED light source; an electronic switch,controllable circuit breaker, or other switching device for turning anappliance on and off; a plug-in load control device, controllablereceptacle, or controllable power strip for controlling one or moreplug-in loads; a motor control unit for controlling a motor load, suchas a ceiling fan or an exhaust fan; a drive unit for controlling amotorized window treatment or a projection screen; motorized interior orexterior shutters; a thermostat for a heating and/or cooling system; atemperature control device for controlling a setpoint temperature of anHVAC system; an air conditioner; a compressor; an electric baseboardheater controller; a controllable damper; a humidity control unit; adehumidifier; a water heater; a pool pump; a TV or computer monitor; anaudio system or amplifier; a generator; an electric charger; electricvehicle charger; and an alternative energy controller.
 117. The loadcontrol system of claim 116, wherein the second load control devicecomprises a different one of the plurality of possible load controldevices.
 118. The load control system of claim 107, wherein the inputdevice comprises a wireless transmitter adapted to transmit wirelesssignals directly to the first and second controllers.
 119. The loadcontrol system of claim 118, wherein the wireless signals comprises RFsignals, the first controller operable to transmit RF signals to thesecond controller, the second controller operable to transmit a thirddigital message to the third and fourth load control devices via thesecond circuit wiring in response to the RF signals received from thefirst controller.
 120. The load control system of claim 107, wherein theinput device comprises a wired transmitter operable to transmit controlsignals to the first and second controllers via a wired control link.121. The load control system of claim 107, wherein the input devicecomprises one of: an occupancy sensor, a vacancy sensor, a daylightsensor, a temperature sensor, a humidity sensor, a security sensor, aproximity sensor, a keypad, a battery-powered remote control, a key fob,a personal digital assistant, a cell phone, a smart phone, a tablet, apersonal computer, a timeclock, an audio-visual control, a safetydevice, a fire protection device, a water protection device, a medicalemergency device, and a central control transmitter.
 122. A load controlsystem for controlling the power delivered from an AC power source to anelectrical load, the system comprising: a load control device adapted tobe coupled to the electrical load for controlling the power delivered tothe electrical load; and a controller adapted to be coupled in serieselectrical connection between the AC power source and the load controldevice to conduct a load current from the AC power source to theelectrical load, the controller operable to produce a phase-controlvoltage that is received by the load control device, wherein thephase-control voltage comprises an AC voltage that is characterized by aconduction period for a portion of each half-cycle; wherein thecontroller is operable to transmit digital messages to the load controldevice for controlling the power delivered to the load by encodingdigital information in timing edges of the phase-control voltage, thecontroller operable to interrupt a first digital message that is beingtransmitted in order to transmit a second digital message to the loadcontrol device such that the controller does not transmit the entiretyof the first digital message.
 123. The load control system of claim 122,wherein the phase-control voltage generated by the controller has anumber of sequential data patterns, each data pattern having a firsttiming edge at a predetermined reference edge time during a firsthalf-cycle and a second timing edge at a data edge time during a secondsubsequent half-cycle, such that an offset time period exists betweenthe reference edge time and the data edge time of each data pattern, thecontroller operable to transmit digital messages to the load controldevice for controlling the electrical load by controlling the offsettime period in each of the sequential data patterns.
 124. The loadcontrol system of claim 123, wherein the controller is operable totransmit a start symbol to begin transmitting a digital message bycontrolling the phase-control voltage to have a third timing edge at afirst start symbol edge time during a third half-cycle and a fourthtiming edge at a second start symbol edge time during a fourthsubsequent half-cycle, such that a start symbol offset time periodexists between the first start symbol edge time and the second startsymbol edge time, the third and fourth half-cycles occurring before thefirst and second half-cycles, the start symbol offset time period notbeing equal to any of the possible offset time periods that may existbetween the reference edge time during the first half-cycle and the dataedge time during the second half-cycle.